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200M/06-99-991212 


II E  R  E  D  I  T  Y 


BY 


C.    W.    SALEEBY,    M.D. 

AVTHOR  OF 
««THK  CYCLE  OF  LIFE,"   "EVOLUTION  THK  MASTKR-KKY,"  ETC. 


NEW    YOHK 

FREDERICK    A.   STOKES   COMl'ANV 

PUBLISHERS 


Printed  by  Ballantyxe,  Hanson  c->  Co. 
At  the  Ballautyne  I'ress 


CONTENTS 


CHAP. 

I.  Introductory 

II.  The  Modes  of  Keproduction 

III.  The  Facts  and  Function  of  Sex 

IV.  The  Biometric  Study  of  Heredity     . 
V.  The  Facts  and  Laws  of  Variation    . 

VI.  The  Origin  of  Variations  . 

VII.  Mendelism 

VIII.  Reversion 

IX.  The  Theories  op  Heredity  . 

X.  The  Inheritance  of  Acquirements     . 

XI.  The    Relative    Importance    of    Heredity 
Environment 

XII.  Heredity  and  "  Physical  Degeneration  " 

XIII.  Heredity  and  Disease  .... 

XIV.  Mental  Heredity 

Subject  Index 

Index  to  Names 


AND 


PACK 

9 
17 
24 
39 
47 
49 
60 
64 
68 
71 

84 
92 
103 
115 
117 
118 


vU 


HEREDITY 


CHAPTER   I 

INTRODUCTORY 

Heredity  is  a  general  term  which  expresses  the  fact 
that  the  individuals  of  all  animal  and  veo^etable 
species  tend  to  beget  f  heir  like ;  "  as  is  very  natural," 
we  feel  inclined  to  add.  This  comment  expresses,  in 
popular  language,  the  conviction  that  heredity  is  a 
"law  of  Nature,"  that  it  results  from  the  action  of 
constant  causes  which  may  be  capable  of  analysis. 
We  expect  to  find  the  child  like  his  father,  partly 
because  we  have  frequent  experience  of  this  like- 
ness ;  but  we  also  feel  that,  had  we  had  no  experi- 
ence of  it,  we  would  have  predicted  its  occurrence. 
It  "stands  to  reason"  that  a  child  must  resemble  his 
father  in  greater  or  less  degree;  and  it  will  be  our 
business  in  the  following  pages  to  inquire  into  the 
manner  of  a  sequence  so  reasonable. 

But,  on  the  other  hand,  the  child,  when  he  grows 
up,  is  not  found  to  be  his  father's  "double."  In 
some  measure,  however  slight,  he  differs.  This  dif- 
ference might  be  attributed,  in  all  cases  of  sexual 
reproduction,  to  the  fact  that  the  child  is  his 
mother's   child   as   well   as   his  father's.      But  even 


10  HEREDITY 

where  the  new  individual  has  but  one  parent,  as 
in  cases  of  what  is  called  parthenogenesis,  it  is  not 
an  exact  replica  of  that  parent ;  and  the  same  is  true 
even  where  sex  is  unknown  and  reproduction  is  ob- 
served in  its  simplest  form.  This  difference  between 
the  begetting  and  the  begotten  might  conceivably  be 
due  to  the  fact  that  the  surrounding  circumstances 
or  environment  of  the  one  were  not  precisely  iden- 
tical with  those  of  the  other.  But  even  when  the 
environment  is  the  same  for  both,  this  difference  is 
still  found,  and  we  express  it  by  the  general  term, 
Variation. 

This  fact,  also,  is  one  of  constant  experience ;  but 
our  opinion  of  it  is  not  that  it  "  stands  to  reason,"  but 
rather  that  it  is  irrational.  We  incline  to  think  that 
heredity  is  the  "  law,"  variation  the  "  accident,"  or 
the  exception  to  the  law.  Strictly  speaking,  we 
fancy,  there  "ought  to  be"  no  such  thing  as  varia- 
tion ;  but  of  course  it  is  unreasonable  to  expect  that 
heredity  shall  always  be  perfect,  and  "  something  or 
other  "  is  doubtless  often  apt  to  mar  its  accuracy,  thus 
leading  to  that  anomalous  (or,  in  English,  lawless) 
occurrence  which  we  call  variation. 

On  second  thoughts,  however,  we  see  that  our 
notions  are  quite  unphilosophic.  Causation  is  non- 
versal ;  and  variations  cannot  be  regarded  as  "  flukes  " 
or  flaws  in  heredity,  but  must  be  subject  to  laws  of 
their  own.  It  will  be  part  of  our  business,  then,  in 
this  book  to  ask  ourselves  whether  variation,  as  well 
as  heredity,  does  not  "  stand  to  reason,"  in  the  sense 
that  it  is  capable  of  a  rational  explanation. 

In  our  study  of  these  matters,  we  might  save  our- 
selves much  trouble  by  the  adoption  of  a  metaphorical 


INTRODUCTORY  11 

mode  of  speech.  The  fact  that  it  saves  us  trouble 
should  put  us  on  our  guard,  there  being  no  royal 
road  to  knowledge,  least  of  all  by  the  way  of  meta- 
phor. Nevertheless  we  constantly  find  ourselves 
talking,  in  fine  language,  of  heredity  and  varia- 
tion as  two  "  forces  " — that  blessed  word  !  These 
"  forces  "  are  "  inherent  in  living  matter  " — a  phrase 
which  really  means  that  we  intend  to  save  ourselves 
the  trouble  of  asking  how  they  come  to  be  "  inherent " 
— and  there  is  eternal  opposition  between  them.  The 
one  "  force  "  is  ever  seeking — since  we  have  got  so  far 
as  to  call  heredity  a  "  force,"  we  may  as  well  personify 
it — to  preserve  the  type,  whilst  the  aim  of  the  other 
is  to  alter  it.  Sometimes  the  one  all  but  vanquishes 
the  other;  sometimes  they  agree  to  a  compromise. 
.  .  .  This  may  be  poetry,  or  journalese,  or  several 
other  things,  but  it  is  certainly  not  science,  or,  at 
any  rate,  not  adequately  scientific.  Whilst  passing 
this  stricture  upon  a  common  manner  of  expressing 
the  facts  in  question,  we  may  yet  admit  that  it  has 
a  certain  symbolic  value,  and  may  be  employed  on 
occasion,  as  long  as  we  clearly  understand  that  our 
language  is  not  literal  but  metaphorical.  For  in- 
stance, we  shall  see  that  this  symbolising  of  here- 
dity and  variation  as  opposing  but  complementary 
forces  is  of  value  in  the  comparison  between  the 
man  and  society — the  individual  organism  and  the 
social  organism.  Plainly  the  conservative  forces  of 
society  are  the  analogue  of  heredity,  and  the  liberal 
forces  are  the  analogue  of  variation ;  concerning 
which  we  must  say  much  more  anon. 

There   is   yet   another   mode    of    conceiving    the 
facts.     This   may   be   described   as    an    attempt    to 


1 2  HEREDITY 

base  a  defence  of  a  non-scientific  doctrine  upon  a 
present  defect  in  scientific  knowledge.  Our  know- 
ledge of  the  causes  of  variation  is — or,  rather, 
very  recently  was — extremely  uncertain  and  scanty. 
Upon  this  evanescent  circumstance  is  erected  some 
such  theory  as  the  following :  Heredity  is  un- 
doubtedly a  "  law  of  Nature,"  and  may  some  day  be 
completely  explained  by  science.  But  variation, 
on  the  other  hand,  is  found  inexplicable  by  science 
— cannot  be  reduced  to  law.  Now  without  varia- 
tion there  can  be  no  organic  evolution,  as  men  of 
science  themselves  assert.  But  organic  evolution, 
ever  making  for  progress,  is  clear  evidence  of 
Purpose  behind  things.  Hence  we  may  accept  the 
theory  of  organic  evolution,  which  it  is  no  longer 
possible  to  doubt ;  but  must  believe  that  Creative 
Design  is  not  incompatible  with  it.  The  Deity, 
however,  acts  not,  as  we  used  to  think,  by  instan- 
taneous creation,  but  by  gradual  creation  through 
evolution.  The  evolutionary  process  is  directed 
towards  the  ultimate  purpose  by  the  gradual  intro- 
duction of  such  variations  as  (being  perpetuated  by 
heredity)  make  ever  for  progress.  This  is  the 
reason  why  men  of  science  cannot  explain  variation ; 
and  since  the  whole  process  of  organic  evolution 
depends  upon  variation,  they  will,  sooner  or  later, 
be  compelled  to  recognise  the  Divine  Hand  as  the 
prime  mover  which  is  above  all  law.  Thus  are 
orthodoxy  and  evolution  reconciled ;  and  the 
doctrine  of  teleology,  or  purpose,  or  final  causes 
is  found  to  be  indispensable  to  the  adequate 
statement  of  the  scientific  theory.  .  .  .  No  direct 
and  present  criticism  of  this  position  is  necessary ; 


INTRODUCTORY  1 .3 

but  we  shall  devote  much  space  to  a  discussion 
of  the  causes  of  variation,  recognising  that  this 
question  is  absolutely  fundamental  to  the  theory  of 
oroanic  evolution. 

And  here  it  is  proper  to  insist  upon  the  im- 
portance of  our  subject.  Heredity  is,  of  course, 
a  very  interesting  matter,  and  so  is  the  occur- 
rence of  variation  side  by  side  with  heredity. 
But  we  study  these  things  to-day  in  a  very  different 
attitude  from  that  of,  say,  a  hundred  years  ago; 
for  we  know  their  signiticance,  their  bearing  upon 
much  greater  matters.  The  astronomer  of  the 
fifteenth  or  sixteenth  century  might  be  interested 
in  tracing  the  exact  movements  of  a  planet. 
These  were  facts  of  Nature  ;  but,  if  they  had  any 
ulterior  significance,  it  was  only  in  illustrating  the 
habits  and  customs  of  the  great  Spirits  which  even 
Kepler  supposed  to  inhabit  and  drive  the  heavenly 
bodies.  But  nowadays,  thanks  to  Kepler  and 
Galileo  and  Newton,  the  astronomer  knows  the 
laws  of  motion  and  gravitation,  and  the  movements 
of  a  planet  mean  something  for  him.  Similarly 
the  facts  of  heredity  and  variation  mean  something 
for  the  biologist  of  to-day,  and  he  studies  them 
hardly  for  themselves  at  all,  but  because  of  their 
bearing  on  organic  evolution.  Now  organic  evo- 
lution is  not  only  the  leading  fact  of  biology,  but 
is  the  basis  on  which  Herbert  Spencer  re-erected 
the  sciences  that  spring  from  biology,  such  as  the 
science  of  mind,  the  science  of  society,  and  the 
science  of  morality.  Hence  the  importance  of 
heredity  and  variation  is  cardinal,  their  elucida- 
tion constituting  a  very  corner-stone   in  that  great 


14  HEREDITY 

structure  of  organised  and  unified  knowledge  of  whicli 
the  theory  of  evolution  is  the  architectonic  principle. 

In  discussing  the  problems  of  heredity,  it  is 
necessary  very  fully  to  consider  certain  changes 
which  are  found  to  occur  in  all  individual  organisms, 
animal  and  vegetable.  These  changes  are  the  result 
of  the  individual  experience — the  result  of  the  series 
of  relations  between  the  individual  and  the  environ- 
ment. Considered  from  this  point  of  view,  they 
might  be  called  adaptations,  since  they  may  all  be 
included  under  the  products  of  adaptation.  Other 
names  may  be  employed.  These  changes  necessarily 
cause  each  individual  to  vary  from  the  type  of 
its  species,  from  even  its  immediate  ancestors,  its 
brothers  and  its  sisters.  Hence  they  might  be  called 
variations.  But  if  we  used  this  term  it  would  be 
necessary  to  employ  qualifying  adjectives,  so  as  to 
point  the  distinction  between  these  variations  and 
those  which  depend  upon  the  innate  or  germinal 
characters  of  the  individual.  These  last  might  be 
termed  blastogenic  variations,  whilst  the  changes 
produced  in  the  individual  body  by  its  converse  with 
its  surroundings  might  be  called  somatogenic.  But 
I  do  not  propose  to  employ  these  terms  at  all,  my 
reason  being  that  they  do  not  adequately  emphasise 
the  cardinal  and  all-important  distinction  (as  we 
now  see  it)  between  innate  and  acquired  characters. 
Hence  the  term  variation  will  be  strictly  confined 
hereafter  to  those  changes  from  the  specific  type 
which  are  innate  and  which  must  now  be  regarded 
as  really  not  distinct  in  origin  from  the  characters 
which  are  obviously  derived  from  the  parent.     Those 


INTRODUCTORY  1 .5 

so-called  somatogenic  variations,  however,  which 
depend  not  upon  anything  derived  from  the  parent, 
save,  perhaps,  the  inherited  power  of  adaptability, 
will  not  be  called  variations  at  all,  but  will  alwavs  be 
termed  acquirements.  The  more  familiar  phrase 
is  acquired  characters,  but  I  follow  Mr.  Archdal] 
Reid  in  using  the  shorter  and  quite  unequivocal  word. 

Accepting  this  terminology,  then,  we  have  to 
consider  acquirements  as  characters  which  may 
often  be  indistinguishable,  or  all  but  indistinguish- 
able, from  true  variations,  since  these,  though  innate, 
may  not  appear  for  years ;  but  which  are  always  to 
be  distinguished  in  theory,  not  only  because  they 
have  a  totally  different  origin,  but  also  because  they 
have  totally  different  consequences.  Variations — 
i,e.  new  inborn  characters — are  unquestionably  trans- 
missible by  heredity,  else  there  could  scarcely  be  any 
organic  evolution ;  but  the  transmission  of  acquire- 
ments is  a  matter  of  keen  controversy,  and  the 
measure  of  its  occurrence,  if  it  occurs  at  all,  must  be 
carefully  considered  in  a  special  chapter.  Obviously 
the  question  is  of  cardinal  importance,  not  only  to 
the  man  of  science,  but  also  to  the  man  of  action,  for 
our  practice  must  be  gravely  affected,  accordingly  as 
we  believe  that  the  results  of  education  can  or  can 
not  be  transmitted  to  our  children.  If  they  can,  one 
method  of  ennobling  our  race  is  clearly  indicated ;  if 
they  cannot,  another  and  a  very  different  method  is 
as  clearly  demonstrated.  ^ 

Our  subject  might  thus  conveniently  be  arranged 
under    three    leading    terms  —  heredity,    variation, 

1  See  ''  The  Future  Evolution  of  Man,"  in  the  volume,  "  Orcranic 
Evolution." 


16  HEEEDITY 

acquirements.  In  discussing  each  of  these,  we  are 
concerned  chiefly  with  bodily  or  physical  characters. 
But  we  would  do  very  ill  to  study  only  these  and 
there  to  rest  content.  It  will  be  necessary  thereafter 
briefly  to  introduce  the  consideration  of  the  facts  and 
possibilities  of  mental  heredity,  mental  variation, 
mental  acquirements.  In  so  doing  we  not  only 
complete  our  study  of  the  subject,  not  only  consider 
matters  of  great  interest  in  themselves,  but  are  also 
preparing  ourselves  for  the  scientific  study  of  the 
human  mind,  the  cardinal  feature  of  this  study 
to-day  being  its  recognition  of  the  fact  that  man's 
mind  is  not  a  prime  fact,  but  has  a  history. 

One  other  aspect  of  this  great  study  of  heredity 
must  also  gain  our  attention.  The  inheritance  of 
disease — disease  of  body  and  disease  of  mind — is  a 
matter  of  vast  practical  importance.  On  none  other 
is  the  public  more  constantly  misinformed,  so  influ- 
enced by  the  erroneous  ideas  of,  say,  forty  years  ago. 
Furthermore,  the  study  of  inheritance  of  disease,  and 
also  the  inheritance  of  immunity  to  disease,  is  of 
great  scientific  interest,  for  it  throws  light  not  only 
upon  the  nature  of  heredity  itself,  but  also  upon  the 
manner  in  which  the  existing  types  and  races  of 
mankind  have  been  affected  by  the  incidence  of 
disease  in  the  past.  It  has  been  left  to  a  dis- 
tinguished medical  observer,  Mr.  Archdall  Keid,  to 
show  how  disease  has  acted,  and  is  still  acting, 
through  heredity,  as  an  instrument  of  natural  selec- 
tion, in  virtue  of  which  mankind  is  constantly  tend- 
ing to  become  more  and  more  immune  to  the  attacks 
of  the  lowly  vegetable  organisms  which  are  the  active 
causes  of  nearly  all  disease. 


THE   MODES    OF    REPRODUCTION  17 

CHAPTER   II 

THE    MODES   OF   REPRODUCTION 

A  NECESSARY  preliminary  to  the  study  of  heredity 
is  a  consideration  of  the  elementary  facts  of  repro- 
duction. We  cannot  understand  heredity  unless  we 
know  the  conditions  in  which  it  works.  The  modes 
of  reproduction  in  the  animal  and  vegetable  king- 
doms are  various ;  there  is  a  great  difference  between 
the  reproduction  of  one  of  the  higher  animals  and 
that  of  a  bacillus  which  reproduces  itself  by  simple 
fission,  or  splitting;  but  in  each  and  every  case 
heredity  is  observed.  The  child  of  a  man  is  human, 
the  child  of  a  bacillus  bacillary. 

In  the  most  primitive  modes  of  reproduction  there 
is  no  problem  of  heredity.  We  have  no  difficulty 
in  understanding  why  the  daughter  bacilli  should 
resemble  their  mother.  They  are  their  mother — 
subdivided.  In  the  case  of  those  plants,  again, 
which  propagate  by  separation  of  integral  portions 
of  their  own  person,  there  is  similarly  no  problem. 
The  new  individual  is  simply  a  separated  and  ex- 
tended portion  of  the  old.  Looking  at  such  cases 
we  understand  how  reproduction  may  be  looked 
upon  as  neither  more  nor  less  than  growth  beyond 
the  limits  of  the  individual  organism.  The  laws  of 
this  growth  and  the  circumstances  which  determine 
the  limits  of  the  individual  organism  are  certainly 
worthy  of  study,  but  they  do  not  directly  concern 
the  student  of  heredity.  Therefore,  though  we  shall 
have  occasion  later  to  refer  to  the  simplest  modes  of 


18  HEREDITY 

reproduction,  as  in  the  case  of  the  bacteria,  we  may 
here  leave  them  thus  briefly  noticed,  and  turn  our 
attention  to  the  mode  of  reproduction  which  may  be 
regarded  as  the  next  in  order  of  complexity — repro- 
duction by  gemmation.  This  is  typically  represented 
in  the  yeast  plant.  The  new  individual  springs  from 
the  old  by  a  process  of  budding.  In  the  act  of  birth 
the  relation  of  one  to  the  other  is  the  same  as  that 
of  a  large  soap  bubble  to  a  small  one  apparently 
springing  from  it.  Here  also  the  new  individual  is 
seen  to  be  no  more  than  a  separated  part  of  its 
parent ;  the  likeness  between  the  two  is  so  far 
from  offering  a  problem  as  to  be  necessary  and 
inevitable. 

But  we  journey  for  only  a  very  short  distance 
through  the  animal  and  vegetable  kingdoms  before 
we  come  in  each  case  to  a  mode  of  reproduction 
which  persists,  so  far  as  essentials  are  concerned, 
even  in  the  most  complex  and  youngest  species — 
such  as  man  or  the  oak  —  with  which  we  are 
acquainted. 

In  the  case  of  the  bacillus,  reproduction  involves 
the  total  evanishment  of  the  parent.  The  mother  is 
lost  in  her  daughters.  Not  essentially  dissimilar  is 
the  case  of  the  yeast  plant  or  the  unicellular  ani- 
mals. But  directly  we  leave  these  lowest  forms  we 
find  ourselves  confronted  with  a  totally  different 
state  of  things.  The  parent  is  no  longer  lost  in  her 
offspring,  nor  is  indeed  the  smallest  essential  part  of 
her.  Further,  the  relation  in  size  and  in  realisable 
complexity  between  the  parent  and  that  by  which 
the  parent  is  reproduced,  becomes  almost  incalcul- 
able.    The  reproductive  cell  of  a  woman  is  about  j^ 


THE    MODES    OF    REPRODUCTION  19 

of  an  inch  in  diameter,  yet  her  daughter  may  display 
the  very  tones  of  her  mother's  voice,  her  very  ges- 
tures, even  her  most  intimate  mental  peculiarities. 
Plainly  we  have  now  come  upon  a  problem  indeed  ! 

It  is  our  business,  then,  to  examine,  with  the  utmost 
particularity  which  the  microscope  and  the  modern 
methods  of  staining  organic  tissues  permit,  the 
characters  of  the  minute  but  immeasurably  poten- 
tial cells  by  which  the  higher  animals  and  plants 
reproduce  themselves.  We  shall  find,  as  might  be 
expected,  that  they  tend  to  be  typical  of  cells  in 
general — not  highly  dift'ercntiated.  A  bone  cell,  a 
nerve  cell,  a  liver  cell,  a  muscle  cell,  diflfer  widely 
from  the  typical  cell  form  ;  but  the  cell  which  is 
destined  to  give  rise  to  all  these  forms,  and  a 
thousand  more,  is  comprehensively  typical  of  all 
other  kinds  of  cells,  but  of  none  in  especial. 

Let  us,  then,  consider  a  typical  animal  ovum — not 
of  any  species  in  particular.  It  is  a  minute  globular 
body,  usually  invisible  to  the  naked  eye,  and  is 
bounded  by  a  thin  cell-membrane.  The  body  of 
the  cell  consists  of  a  granular,  semi-solid  substance, 
which  is  alive,  and  which  is  an  example  of  proto- 
plasm— the  "physical  basis  of  life."  Somewhere 
about  the  centre  of  the  cell  there  is  a  minute,  rather 
denser  speck,  which  we  call  the  nucleus.  Stained 
with  appropriate  dyes  this  nucleus  displays  a  net- 
work of  linely  interlacing  fibres.  This  network  takes 
the  dye  colour  deeply,  and  is  therefore  known  as  the 
chromatin  of  the  nucleus.  Weismann  has  taught 
us  to  regard  it  as  the  bearer  of  hereditary  characters. 
Just  beside  the  nucleus — in  the  large  majority  of 
cases — is  a  nmch  smaller  speck  which  is  called  the 


20  HEREDITY 

centrosome,  and  which  apparently  plays  an  important 
part  in  initiating  the  phenomena  of  cell- division. 

Now  it  is  beyond  reasonable  question  the  nucleus 
that  is  the  essential  part  of  the  cell.  The  rest  of  the 
cell  body  has  probably  no  more  than  a  nutritive 
function.  The  changes  in  the  nucleus  which  pre- 
cede, accompany,  and  succeed  the  act  of  reproduc- 
tion must  later  be  described.  But  we  may  be 
permitted  here  to  indulge  in  certain  abstract  con- 
siderations as  to  the  intimate  structure  of  the 
nucleus.  We  have  already  noticed  the  existence 
of  a  special  portion  of  the  nucleus  which  is  readily 
stained  by  suitable  dyes,  and  which  is  therefore 
called  the  chromatin.  Every  division  of  this  and 
every  other  cell  of  any  of  the  higher  animals  and 
plants  is  initiated  by  the  breaking  up  of  the  nuclear 
chromatin  into  a  number  of  separate  rod-like  bodies 
known  as  chromosomes.  When  these  chromosomes 
are  examined  by  the  microscope,  after  treatment 
with  suitable  dyes,  they  are  found  to  contain  a 
number  of  smaller  bodies,  each  of  which  must  be 
regarded  as  a  complex  structure,  "  possessed  of  a 
historic  architecture  that  has  been  elaborated  slowly 
through  the  multitudinous  series  of  generations  that 
stretch  backwards  in  time  from  every  living  indi- 
vidual." These  minute  bodies,  or  microsomes,  can- 
not further  be  resolved  by  the  microscope,  but 
Weismann  assumes  that  each  of  them  in  its  turn 
consists  of  a  number  of  still  smaller  bodies,  which 
he  calls  deterriiinants.  He  has  his  own  names  for 
the  larger  units,  but  it  would  be  of  little  profit  to 
quote  them.  The  concept  of  determinants,  however, 
is  worthy  of  note,  for  Weismann  argues  that  these 


THE    MODES    OF    REPRODUCTION  21 

are  the  structures  of  the  germ-plasm  which  deter- 
mine the  characters  of  the  adult  organism,  and  it 
will  later  be  of  great  importance  to  inquire  as  to 
the  influences  which  any  adult  organism  can  bring 
to  bear  upon  the  determinants  of  the  reproductive 
cells  which  it  bears,  and  by  which  it  is  destined  to 
reproduce  itself.  But  Weismann  regards  it  as  neces- 
sary, and  with  justice,  to  assume  that  even  these 
determinants  are  not  the  ultimate  living  units. 
These  hypothetical  constituents  of  each  determinant 
he  calls  biophores.  They  are  the  ultimate  living 
units.  It  is  not  inconceivable  that  they  may  be 
identical  in  all  living  things. 

Now  Weismann  is  by  no  means  the  first  or  only 
biologist  to  postulate  the  existence  of  the  specialised 
living  units  which  he  calls  determinants.  They  have 
received  at  least  a  dozen  difterent  names  from  as 
many  biologists  during  the  past  forty  years.  But  in 
point  of  fact  the  originator  of  this  conception  was  a 
student  who  approached  biology  from  the  outside. 
It  is  in  Herbert  Spencer's  "  Principles  of  Biology  " 
that  this  idea  is  first  to  be  met,  long  before  we  had 
attained  to  our  present  extended  knowledge  of  the 
reproductive  process.  Furthermore,  the  Spencerian 
conception  has  gained  little  if  at  all  from  the  efforts 
of  the  many  workers  who  have  since  adopted  it. 
Spencer  saw  that,  on  the  one  hand,  the  coll  must 
be  regarded  as  the  raorphological  ^  unit  of  living 
organisms.  On  the  other  hand,  there  must  necessarily 
be  a  chemical  unit,  consisting  of  the  simplest  com- 
bination   of  molecules    capable   of    displaying   life. 

1  Morphology  is  the  science  of  form  in  living  things.     We  owe 
the  term  to  Goethe. 


22  HEREDITY 

This  obviously  corresponds  to  the  biophore  of  Weis- 
mann.  Such  a  unit  would  be  common  to  all  forms 
of  living  matter  :  it  would  have  no  specific  characters. 
But  if  we  consider  the  phenomena  of  repair — as  in 
the  growth  of  a  lizard's  leg  after  amputation,  or  in 
the  development  of  a  begonia  from  a  leaf- fragment 
— we  note  the  existence  of  a  property  which,  in  the 
case  of  repair  of  damaged  crystals,  is  called  polarity. 
Thus  we  may  use  the  term  organic  polarity,  or 
polarity  of  the  organic  units,  to  signify  the  proxi- 
mate cause  of  the  ability  which  organisms  display  of 
reproducing  lost  parts. 

Spencer,  therefore,  supposed  that  the  chemical 
units  combine  into  units  immensely  more  com- 
plex than  themselves,  complex  as  they  are ;  and  that 
in  each  organism  these  physiological  units  pro- 
duced by  this  further  compounding  of  highly 
compound  molecules  have  a  more  or  less  distinctive 
or  "  polar  "  character.  Obviously  the  phenomena  of 
repair,  which  led  Spencer  to  this  most  important  con- 
ception, are  indistinguishable  in  principle  from  any 
other  case  of  heredity.  If,  then,  we  desire  to  track 
down  to  its  hiding-place  the  ultimate  material 
structure  to  which  all  the  phenomena  of  heredity 
and  variation  must  be  referred,  we  find  ourselves 
satisfied  with  the  'physiological  unit  of  Spencer, 
re-named  "gemmule,"  "  plastidule,"  "determinant," 
and  I  know  not  by  how  many  other  terms. 
Recalling  our  study  of  the  typical  nucleus,  we 
remember  that  its  chromatin  is  really  a  collection 
of  chromosomes,  in  which  minute  parts  (microsomes) 
may  be  detected.  Where  the  microscope  fails  us, 
theory  steps  in,  and  argues  that  these  microsomes 


THE    MODES    OF    REPRODUCTION  23 

must  consist  of  the  physiological  units  postulated  by 
Spencer. 

Much  space  has  been  spent  on  this  subject :  firstly, 
because  it  is  satisfactory  to  correlate  theory  with 
actual  structure,  so  far  as  is  possible ;  secondly, 
because  it  is  plainly  necessary  that  we  should  pursue 
our  study  of  the  nucleus  to  the  very  last  limits  ; 
and  finally,  because  this  great  conception  of  physio- 
logical units  has  lately  acquired  a  new  importance — 
clearly  anticipated  by  its  originator — in  relation  to 
the  remarkable  theory  of  variation  which  traces  its 
origin  to  the  work  of  the  Abbe  Mendel  forty  years 
ago,  but  which  has  only  within  the  last  year  or  two 
taken  its  place  as  one  of  the  most  important  of  the 
constructive  efforts  of  modern  biology.^ 

It  wdll  now  be  necessary  for  us  to  study  the  repro- 
ductive cell,  not  in  the  abstract,  but,  so  to  speak,  in 
situ,  as  an  actual  structure  found,  in  given  conditions, 
in  all  but  the  lowest  animals  and  plants.  So  far  as 
is  possible,  we  must  make  our  study  of  heredity  a 
study  of  observed  facts.  The  less  we  talk  al)out 
"  forces "  and  the  more  about  positive  entities  and 
sequences  that  can  be  actually  observed,  the  more 
likely  are  we  to  reach  conclusions  that  will  reward 
our  labours.  Fortunately,  we  live  to-day  not  in 
the  dawn  of  embryology,  which  is  now,  despite  its 
difficulties,  an  astonishingly  luminous  and  con- 
spicuous science. 

One  further  note  may  be  made.  At  first  sight  it 
may  seem  almost  incredible  that  a  heritable  organi- 
sation of  great  complexity  can  iind  its  physical  basis 
in  a  microscopic  ovum  and  in  a  spermatozoon  which 

1  See  Chapter  VII. 


24  HEREDITY 

may  be  only  tooVo^f  '^^  t^®  ovum's  size.  But,  as 
Thomson  observes,  "  it  may,  however,  be  recalled  (1) 
that  the  physicists  report  that  the  image  of  a  Great 
Eastern  filled,  with  framework  as  intricate  as  that  of 
the  daintiest  watch  does  not  exaggerate  the  possi- 
bilities of  molecular  complexity  in  a  spermatozoon, 
whose  actual  size  may  be  less  than  the  smallest  dot 
on  the  watch's  face ;  (2)  that  in  development  one  step 
conditions  the  next,  and  one  structure  often  grows 
out  of  another,  so  that  we  are  not  forced  to  stock  the 
microscopic  germ-cells  with  more  than  initiatives." 


CHAPTER  III 

THE   FACTS    AND    FUNCTION   OF   SEX 

When  we  leave  the  lowest  animals  and  plants  and 
consider  the  many-celled  organisms  we  come  upon 
the  fact  of  sex.  We  find  that  multicellular  organisms 
give  rise  to  special  reproductive  cells,  or  gametes,  one 
kind  of  which  is  produced  by  female  organisms  and 
another  by  male  organisms.  The  former  are  called 
macrogametes  and  the  latter  microgametes  (i.e.  large 
and  small  gametes).  The  older  terms  applied  to 
these  cells  in  the  animal  kingdom  are  ova  and  sper- 
matozoa. These  germ-cells,  or  gametes,  are  highly 
typical  and  representative  living  cells,  having  the 
structure  already  described.  They,  or  rather  their 
nuclei,  form  "  the  material  basis  of  inheritance "  ; 
and  it  is  to  them  that  the  scientific  study  of  heredity 
constantly  refers  us.  The  first  question  we  must  ask 
ourselves  is   as   to   the  origin   of  these   germ-cells. 


THE    FACTS    AND    FUNCTION    OF    SEX  25 

Whence  do  they  come ;  what  is  their  precise  relation 
to  the  individual  who  bears  them  ?  This  question 
and  others  connected  with  it  logically  precede  any 
discussion  as  to  the  meaning  of  the  fact  that  these 
gametes  are  of  two  kinds,  male  and  female.  It  is 
only  in  the  latter  half  of  this  chapter  that  we  shall 
need  to  consider  this  matter.  For  the  present  we 
can  completely  ignore  this  sexual  dili'erence,  and 
need  discuss  neither  the  contrasting  characters  of 
the  two  kinds  of  gamete,  nor  the  mode  of  their 
union,  nor  the  function  served  by  their  differentia- 
tion. These  fascinating  matters  will  be  intelligible 
only  when  we  know  exactly  what  the  gamete  is  and 
whence  derived. 

The  older  fashion  of  expressing  the  facts  —  a 
fashion  perfectly  just  —  was  as  follows.  Consider 
the  single  cell  from  which  any  of  the  higher  animals 
or  plants  is  developed.  (Later  we  shall  see  the  orighi 
of  this  cell.)  It  divides  and  divides  and  ultimately 
forms  a  complete  organism — a  bird  or  a  man  or  a 
tree.  But  certain  of  the  cells  formed  by  these  many 
divisions  have  a  special  function.  They  are  kept 
apart  in  a  particular  portion  of  the  organism ;  and 
they  give  rise  to  cells  which  do  not  serve  the  indi- 
vidual, or,  in  a  sense,  form  any  part  of  its  structure, 
but  which  are  ultimately  shed  and  will  give  rise  to 
new  individuals,  after  union  with  similar  cells  of  the 
opposite  sex. 

This  is  a  true  account ;  but  the  facts  may  be  ex- 
pressed in  a  much  more  significant  fashion.  I  will 
employ  the  words  of  Professor  Arthur  Thomson  : — 

"  From  another  point  of  view  it  may  be  said  with 
equal   accuracy   that    the   fertilised  ovum    [i.e.  the 


26  HEREDITY 

single  cell  from  which  all  the  higher  animals  and 
plants  are  developed]  gives  rise  in  development  to 
two  sets  of  elements — to  the  somatic  cells  [soma — 
the  body],  which  become  differentiated  into  the 
various  tissues  of  the  body,  and  to  a  lineage  of  non- 
specialised  germ-cells,  some  of  which  will  eventually 
be  separated  off  to  begin  a  new  generation." 

Here  we  have  an  idea  of  cardinal  importance. 
Ideally  stated,  the  sequence — actually  observed  in 
many  animals — is  as  follows  : — The  germ-cells  and 
the  body-cells  grow  up  side  by  side.  The  germ-cells 
are  shed  and  give  rise  again  to  a  new  body  and  to 
their  own  undifferentiated  descendants,  which  that 
new  body  temporarily  shelters.  The  germ-cells  are 
"  immortal " ;  the  individual  is  merely  a  temporary 
host  which  shelters  a  few  generations  of  the  germ- 
cells,  whose  unbroken  continuity  constitutes  the 
race.  Plainly  the  likeness  of  daughter  and  mother 
begins  to  be  intelligible.  The  germ-cells  of  the 
mother — which  will  develop  into  her  daughter — are 
directly  continuous  with  the  cells  which  gave  rise 
to  the  body  of  the  mother.  "As  the  sex-cells  in 
an  offspring  are  thus  genetically  continuous  with 
[i.e.  directly  derived  from]  the  parental  sex-cells 
which  gave  rise  to  it,  they  will  in  turn  develop  into 
organisms  like  the  parent — a  conception  fundamental 
to  an  understanding  of  inheritance  and  development." 
On  this  theory  of  Weismann  we  must  regard  each 
individual  as  merely  the  temporary  host  of  the  con- 
tinuous line  of  germ-cells  which  constitute  the  race. 

Now  in  many  of  the  lower  animals  the  actual 
unbroken  sequence  of  the  germ -cells,  from  one 
generation   to    another,   can   positively  be  detected. 


THE    FACTS    AND    FUNCTION    OF    SEX  27 

But  in  higher  animals,  and  notably  in  most  plants, 
the  reproductive  cells  cannot  be  recognised  until  the 
development  of  the  organism  is  considerably  ad- 
vanced. In  such  cases,  then,  it  is  impossible  to 
demonstrate  any  continuity  between  the  germ-cells 
of  an  individual  and  the  germ-cells  of  its  parent. 
But  Weismann  has  shown  that  it  is  not  therefore 
necessary  to  abandon  the  invaluable  concept  of 
continuity.  He  very  reasonably  assumes  that  the 
essential  part  of  each  germ-cell  is  not,  for  instance, 
the  cell-membrane,  or  the  cellular  shape,  but  a  par- 
ticular kind  of  living  matter — the  germ-plasm.  He 
supposes,  then,  that  in  the  development  of  each 
individual  a  portion  of  the  germ-plasm  contained  in 
the  parental  ovum  "is  not  used  up  in  the  formation 
of  the  offspring,  but  is  reserved  unchanged  for  the 
formation  of  the  germinal  cells  of  the  following 
generation,"  There  are  grounds  for  believing,  as  we 
shall  see,  that  the  chromatin  of  the  nuclear  network 
represents  this  germ -plasm.  Though  there  is  not 
always  continuity  of  germ-cells  from  generation  to 
generation — as  there  demonstrably  is  in  many  animals 
— there  is  always,  in  all  the  animals  and  plants  which 
display  this  mode  of  reproduction,  a  "  continuity  of 
the  germi-'plasm" 

This  phrase  must  be  remembered.  It  expresses  a 
theory  of  the  very  highest  importance ;  it  is  sup- 
ported by  a  large  amount  of  evidence,  and  is  posi- 
tively contradicted  by  none ;  ^  it  illuminates  all  our 
conceptions  of  inheritance ;  and  the  inferences  from 
it  are  of  the  first  importance  in  regard  to  the  great 
controversy  as  to  the  inheritance  of  acquirements. 
1  See  Chapter  IX.  "  The  Theories  of  Heredity." 


28  HEREDITY 

If  the  germ-plasm  is  continuous  or  immortal, 
then  the  individual  body  does  not  produce  it,  but 
is  its  host.  Hence  we  are  led  to  inquire  into  the 
relations  between  the  one  and  the  other.  Does  the 
germ-plasm  affect  the  body  that  carries  it  ?  Does 
the  body  affect  the  germ- plasm  ?  The  second  of 
these  questions  will  later  be  considered.  The  first 
is  not  material  to  our  subject. 

Let  us  now  recall  the  fact  that  the  germ-cells,  or 
gametes,  are  male  and  female,  for  this  is  evidently 
a  fact  of  very  great  importance.  But  it  is  not  an 
essential  fact  nevertheless,  for  we  find  that  the 
female  gamete  may  develop  and  give  rise  to  an 
individual  without  the  interposition  of  the  male.  As 
this  is  the  simpler  case  it  falls  to  be  considered  first. 

Reproduction  by  means  of  a  single  (female)  germ- 
cell  is  called  parthenogenesis,  the  nearest  English 
equivalent  of  which  is  virgin-birth.  This  develop- 
ment of  the  female  gamete  without  fertilisation  by 
the  male  is  found  in  many  very  lowly  groups  of  the 
animal  kingdom.  Furthermore,  it  can  be  initiated 
by  artificial  modification  of  the  environment  of  the 
ovum.  Our  business  here,  however,  is  to  discuss 
this  matter  only  in  so  far  as  it  bears  on  heredity. 
If,  then,  we  consider  all  the  known  cases  of  natural 
parthenogenesis,  and  all  the  successful  attempts  to 
induce  parthenogenesis,  what  do  we  find  as  to  the 
occurrence  of  heredity  and  variation  ?  The  case  is 
simpler  than  that  of  bi-parental  reproduction,  and 
should  be  more  intelligible. 

Our  concept  of  the  "  continuity  of  the  germ- 
plasm  "  fully  prepares  us  to  understand  the  fact  of 
heredity   in   cases   of    parthenogenesis.      We    have 


THE    FACTS    AND    FUNCTION    OF   SEX         20 

already  seen  that  heredity  is  inevitable  in  the  one- 
celled  animals  and  plants;  but  Weismann's  idea  of 
the  germ-plasm  as  continuous  and  the  individual  as 
merely  its  temporary  trustee  loads  us  to  look  upon 
heredity  as  equally  inevitable,  even  in  the  case  of 
the  multicellular  organisms.  Now  where,  as  in 
parthenogenesis,  there  is  no  complication,  the  new 
individual  arising  from  the  unassisted  ovum  of  the 
old,  we  might  reasonably  expect  heredity  to  bo  very 
exact  and  variation  either  absent  altogether  or  very 
slight.  In  accordance  with  his  theory  of  the  func- 
tion of  sex — immediately  to  be  considered — Weis- 
mann  taught  that  parthenogenetic  species  do  not 
vary,  cannot  vary,  since  it  is  the  intermingling  of 
sexual  cells  in  bi-parental  reproduction  that,  as  he 
averred,  gives  rise  to  variations. 

This  matter  has,  therefore,  been  carefully  studied 
of  late  years,  and  it  is  now  possible  positively  to 
deny  the  contention  of  Weismann.  Variation  occurs 
abundantly  even  in  asexvxil  and  parthenogenetic 
repi'oduction.  This  is  a  fact  of  cardinal  importance, 
and  must  be  remembered  as  profoundly  aliecting  our 
understanding^  of  the  cause  of  variations.  Havinsf 
carefully  noted  it,  we  are  now  prepared  to  consider 
the  facts  of  heredity  and  variation  as  observed  in 
ordinary  sexual  or  bi-parental  reproduction,  which  is 
so  widely  observed  throughout  the  animal  and  vege- 
table kinsfdoms. 

In  the  first  place,  we  must  discuss  the  observed 
facts  of  this  method  of  reproduction.  We  have 
noted  that  the  gametes,  or  sex-cells,  are  of  two 
kinds,  male  and  female.  Each  of  these  is  a  complete 
cell ;  we  have  seen  that   the  ovum — in  certain  low 


30  HEREDITY 

forms — may  actually  give  rise,  unaided,  to  a  new 
individual :  and  there  is  some  evidence  to  show 
that  the  spermatozoon  has  a  similar  potentiality. 

Now  let  us  recall  what  was  said  as  to  the  typical 
structure  of  a  cell.  We  saw  that  the  cell  nucleus 
contains  a  certain  stainable  structure  called 
chromatin.  Now,  when  any  cell  divides,  it  is 
found  that  the  chromatin  breaks  up  into  a  number 
of  separate  portions  called  chromosomes.^  The 
number  of  these  chromosomes  is  invariable  for  every 
cell  of  any  species  of  animal  or  plant.  If  eight 
or  sixteen  be  the  number,  eight  or  sixteen  re- 
spectively are  always  observed  in  the  division  of 
any  cell  of  any  part  of  the  body. 

Let  us  suppose,  then,  that  sixteen  is  the  charac- 
teristic number  of  the  species  we  are  considering. 
The  act  of  bi-parental  reproduction  consists  in 
the  intimate  blending  of  the  nucleus  of  the  ovum 
with  the  nucleus  of  the  spermatozoon.  The  result 
would  be  the  formation  of  a  new  cell — the  cell  from 
which  the  new  individual  is  to  arise — which  would 
contain  thirty-two  chromosomes  in  its  nucleus ; 
and  at  every  generation  the  number  of  chromosomes 
proper  to  the  species  would  be  doubled.  But  a  re- 
markable fact  was  discovered  by  Van  Beneden.  He 
found  that  every  ovum  and  spermatozoon  is  formed 
by  the  division  of  what  is  called  a  mother-germ-cell 
(male  or  female).  This  division  is  of  a  unique 
character ;  for  it  results  in  the  formation  of  cells — 
the  actual  ova  or  spermatozoon — which  contain 
only  one-half  the  number  of  chromosomes  charac- 

1  Not  to  be   confused  with  the  centrosome,  which  usually  lies 
near  the  nucleus. 


THE    FACTS    AST)    FUNCTION    OF    RFX  31 

teristic  of  the  cells  of  the  species.  In  the  case  we  arc 
considering,  the  mother-germ-cell  would  contain 
sixteen  chromosomes ;  but  it  undergoes  what  is 
now  known  as  a  "  reducing  division,"  effecting  the 
"  reduction  of  the  chromosomes,"  so  that  the  actual 
ovum  or  spermatozoon  contains  only  eight  chromo- 
somes in  its  nucleus.  When  the  nucleus  of  the 
spermatozoon  and  that  of  the  ovum  unite,  the 
eight  are  added  to  the  eight,  and  there  is  formed  a 
new  cell  whose  nucleus  contains  sixteen  chromo- 
somes again.  From  this  cell  arise  all  the  cells  of 
the  body  of  the  new  individual,  and  each  contains 
sixteen  chromosomes,  as  did  those  of  the  body 
of  its  parent.  These  are  observed  and  veritied 
facts.^  Thus  Huxley  was  right  in  his  prophecy  of 
1878 :  "  It  is  conceivable,  and  indeed  probable,  that 
every  part  of  the  adult  contains  molecules  derived 
both  from  the  male  and  from  the  female  parent ; 
and  that,  regarded  as  a  mass  of  molecules,  the  entire 
organism  may  be  compared  to  a  web,  of  which  the 
warp  is  derived  from  the  female  and  the  woof  from 
the  male."  ''  What  has  since  been  gained,"  says 
Professor  E.  B.  Wilson,  "  is  the  knowledge  that  this 
web  is  to  be  sought  in  the  chromatic  substance  of 
the  nuclei,  and  that  the  centrosome  is  the  weaver 
at  the  loom." 

Reasoning  upon  these  facts.  Professor  Weismann 

^  A  wholly  new  importance  has  quite  lately  been  conferred  upon 
this  subject  by  the  researches  of  Professor  Farmer  and  Messrs. 
Walker  and  Moore.  They  have  made  the  most  important  discover}- 
that  the  cells  of  all  malignant  tumours — cancers  and  sarcomas — 
exhibit  a  mode  of  division  similar  to  that  of  raothcr-gorm-cclls. 
This  goes  very  far  to  ex-jtlain  the  peculiar  jJrojHirtics  of  malignant 
cells,  and  sets  us  upon  the  right  line  for  the  complete  cxplauat  ion 
of  malignant  tumours. 


32  HEREDITY 

constructed  a  most  ingenious  and  plausible  and 
reasonable  theory  in  which  most  of  us  have  fully 
believed  until  recent  times.  The  theory  was  that 
the  sole  cause  of  variations  in  all  organisms  save  the 
very  lowest  is  the  intermixture  of  two  somewhat  dis- 
similar germ-plasms  in  the  act  of  bi-parental  repro- 
duction. Observe  that  each  gamete  loses  half  its 
chromosomes,  and  the  new  cell  formed  from  the  two 
thus  contains  only  a  portion  of  the  elements  of  each. 
The  natural  supposition  was  that  there  is  a  germinal 
selection  of  parental  characters ;  some  are  taken, 
others  left :  and  hence  the  new  individual  must  vary 
from  either  of  his  parents,  and  need  by  no  means 
necessarily  "strike  an  average"  between  them.  In 
other  words,  the  function  of  sex  is  the  production  of 
variations ;  and  the  known  facts  seem  to  afford  a 
ready  explanation  of  the  manner  in  which  such 
variations  arise. 

Nevertheless,  this  most  satisfactory  and  consistent 
theory  must  be  totally  repudiated.  It  is  not  enough 
in  science,  though  it  has  alwavs  sufficed  in  meta- 
physics  and  in  theology,  that  a  theory  be  self- 
consistent  and  logical.  The  contention  of  science  is 
that  the  theory  must  be  consistent  not  merely  with 
itself,  but  also  with  the  facts.  We  may  remember 
Huxley's  joke  as  to  Spencer's  idea  of  a  tragedy :  "  A 
deduction  killed  by  a  fact."  That  is  the  irremediable 
accident  that  has  befallen  Weismann's  explanation 
of  the  origin  of  variation  and  the  function  of 
bi-parental  reproduction. 

In  the  first  place,  it  is  found,  on  a  priori  mathe- 
matical grounds,  that  the  effect  of  amphimixis — as 
Weismann  calls  the  process  of  nuclear  conjugation — 


THE    FACTS    AND    FUNCTION    OF    SKX  33 

sliould  be  rather  regression  to  the  racial  average,  or 
mean,  than  "  progressive  variation  "  from  it.  Again, 
it  is  found,  as  we  have  already  seen,  that  partheno- 
genetic  and  asexual  reproduction  are  accompanied  by 
abundant  variation,  though,  on  the  theory  of  Weis- 
mann,  there  should  be  none  whatever  in  such  cases. 
Further,  the  biometricians — the  new  school  of  biolo- 
gists who  study  the  facts  by  the  most  rigid  mathe- 
matical methods — have  shown  that,  in  general  terms, 
the  descree  of  resemblance  between  individual  struc- 
tures  sexually  produced  and  between  individual 
structures  asexually  produced^  is  the  same:  a  fact 
which  "  renders  it  impossible  to  accept  Weismann's 
view  that  one  of  the  results  produced  by  the  differen- 
tiation of  animals  and  plants  into  two  sexes  is  an 
increase  in  the  variability  of  their  offspring." 
Further,  the  variation  of  parthenogenetically  pro- 
duced "  brethren  "  amongst  one  of  the  Aphides  and 
the  Daphnia  is  found  to  be  not  dissimilar  to  that 
observed  as  the  result  of  sexual  reproduction.  And 
measurements  of  a  very  lowly  animal,  the  paramoe- 
cium,  in  which  sex  has  not  been  evolved  at  all,  point  to 
the  same  conclusion,  viz.  that,  as  Karl  Pearson  says, 
"Variability  is  not  a  product  of  bi-parcntal  inherit- 
ance. .  .  .  Whatever  be  the  physiological  function 
of  sex  in  evolution,  it  is  not  the  production  of 
greater  variability."  Or,  to  quote  the  actual  words 
of  Mr.  Archdall  Reid,  from  whom  I  have  taken  the 
previous  quotation  :  "  Though  nearly  all  biologists 
have  supposed  that  progressive  ^  variation,  and  there- 

1  See  p.  45. 

2  It  may  here  be  noted  in  anticipation  that  progressive  and  re- 
gressive are  terms  applied  to  variations  accordini;ly  as  whether 
they  tend  away  from  or  back  to  the  type  of  the  species.  There  is 
no  moral  significance  in  the  terms. 

C 


34  HEREDITY 

fore  [organic]  evolution,  is  largely  due  to  bi-parental 
reproduction,  there  is,  in  fact,  in  the  whole  range  of 
biological  literature  not  one  iota  of  evidence  which 
supports  that  view.  Men,  as  in  so  many  instances, 
have  accepted  a  dogma  without  proof,  and  have  held 
it  without  inquiry." 

What,  then,  is  the  function  of  sex  in  relation  to 
heredity  ?  That  there  is  a  function  we  can  scarcely 
doubt ;  for  though  we  know  other  uses  for  sex,  as  in 
human  life  which  is  incalculably  widened  thereby,  it 
is  not  possible  to  explain  the  earlier  stages  of  sex  by 
reference  to  any  future  advantages,  moral  or  social  or 
other,  such  as  we  now  enjoy. 

We  have  already  found  that  the  exceedingly  plau- 
sible and  attractive  theory  of  Weismann  is  unten- 
able. If  bi-parental  reproduction  is  not  a  cause  of 
variations,  it  must  nevertheless  bear  some  relation 
to  them.  Knowing  what  we  do  of  the  manner  in 
which  sexual  cells  unite  to  form  a  new  individual, 
it  is  inconceivable  that  sexual  reproduction  has  no 
relation  to  heredity  and  variation. 

The  answer  appears  to  be  that  bi-parental  repro- 
duction is  a  means  of  preserving  the  racial  type. 
The  true  answer  is  exactly  the  opposite  of  that  given 
by  Weismann.  As  this  subject  is  more  adequately 
and  recently  considered  by  Archdall  Reid  than  by 
any  other  writer,  I  will  quote  largely  from  him  in 
considering  it.  But  here  let  me  make  an  observa- 
tion of  my  own.  In  my  opinion,  Mr.  Reid  has  con- 
clusively proved  that  bi-parental  reproduction,  by 
"  planing  away  useless  variations,"  "  contributes  to  the 
stability  of  the  species."  Now  a  school  of  observers 
— Professor  Karl   Pearson  and   his   followers — who 


THE    FACTS    AND    FUNCTION    OF    SEX  35 

study  biological  problems  from  a  standpoint  of  i  heir 
own,  and  who  have  frequently  disposed   of  various 
hypotheses  widely  held,   have   lately  devoted   their 
attention  to  the  facts  of  sexual  selection,^  and,  on 
this  occasion,  have  gone  far  to  confirm  and  supple- 
ment the  conclusions  of  Darwin.     They  have  shown 
that,  in  all  cases  hitherto  examined,  there  is  a  prin- 
ciple of  homogaviy,  the   mating  of  like  with   like. 
It  hardly  needs  saying  that  this   observed   fact   of 
sexual   reproduction   consorts  completely    with    the 
view  that  amphimixis  is  a  means  of  ensuring  the 
stability  of  the  species.     The  discovery  of  the  fact 
of  homogamy  is  absolutely  incompatible  with  Weis- 
mann's  interpretation  of  amphimixis,  but  most  sig- 
nally confirms  this  new  interpretation  of  the  facts  of 
sex,  which  has  been  reached  by  quite  another  route. 
Let  us  now  make  note  of  Mr.  Reid's  chief  points; 
previously  reminding  ourselves  of  the  meaning  of  the 
terms  progressive  and  regressive  as  applied  to  varia- 
tions.    We  have  seen  that  amphimixis  is  not  a  cause 
of  progressive  variations.     On  the  contrary,  there  is 
much  evidence  which  shows  that  '*  bi-parental  repro- 
duction tends  to  eliminate  the  characters  in  which 
parents  differ,  and  to  leave  unafi'ected  those  in  which 
they  agree."     It  is  a  matter  of  common  observation 
that  exceptional  peculiarities  of  parents  tend  to  dis- 
appear.    But  if  both  parents  are  tall  and  dark,  say, 
or  short  and  fair,  these   variations  tend  to  be  per- 
petuated   l)y   amphimixis.      There   is   no   evidence 
that  bi-parental  reproduction  is  connected  with  pro- 
gressive variations  as  cause  and  effect ;  whenever  it 

1  This  very  import :uil   subject  is  dealt  with  in  Cliap.  vi.  of  tho 
volume  ou  "  Orgauic  Evolution." 


36  HEREDITY 

acts  at  all  as  a  cause  of  variations,  they  are  regressive 
and  not  progressive :  back  to  the  type  and  not  away 
from  it. 

When  precise  experiments  are  made,  it  is  found 
that  the  mating  of  different  varieties  or  species 
always  tends  towards  great  reversion — not  to  the 
immediate  ancestry,  but  to  the  remote  ancestral 
form.  All  the  special  characters  tend  to  disappear. 
"  The  ancestral  form  common  to  both  varieties,  even 
if  it  be  separated  from  the  crossed  descendants  by 
thousands  of  generations,  tends  to  reappear."  Mr. 
Reid  quotes  a  very  large  number  of  instances,  animal 
and  vegetable,  from  Darwin,  Cossar  Ewart,  and  other 
observers.     These  might  be  indefinitely  multiplied. 

Now  Mr.  Francis  Galton  has  long  ago  provided  us 
with  evidence  and  conclusions  which  nicely  consort 
with  the  theory  of  the  function  of  amphimixis  which 
I  am  trying  to  expound.  Mr.  Galton  studied  inherit- 
ance in  animals,  and,  very  widely,  in  man ;  including 
in  his  purview  moral  and  mental  as  well  as  physical 
characters.  He  was  thus  able  to  enounce  a  well- 
attested  law  or  principle,  which  he  termed  "regres- 
sion towards  mediocrity."  [His  observations  were 
confined  to  the  higher  species,  in  all  of  which  bi- 
parental  reproduction  is  universal.]  Let  us  take, 
then,  one  or  two  simple  instances  derived  from  the 
inheritance  of  mind,  which  illustrate  this  principle 
of  regression  towards  mediocrity.  On  the  average, 
the  children  of  a  genius  tend  to  have  something 
less  than  their  father's  power,  but  yet  to  be  above 
the  mental  average  of  the  race.  Similarly  the  chil- 
dren of  the  criminal  tend  to  be  less  vicious  than 
he,  though  morally  inferior  to  the  average  man.     In 


THE    FACTS    AND    FUNCTION    OF    SEX  37 

the  case  of  physical  characters,  also,  this  principle 
is  constantly  illustrated.  It  is  obvious  that  the 
principle  is  explicable  in  strict  accordance  with  the 
theory  that  the  function  of  amphimixis  is  to  ensure 
stability  of  the  type — that  is,  be  it  well  noted,  the 
type  of  the  race,  not  the  new  and  varying  parental 
type.^  Indeed,  every  kind  of  evidence,  old  and  new, 
tends  to  support  this  new  interpretation  of  the  func- 
tion of  amphimixis.  Mr.  Reid  is  surely  justified  in 
saying  that,  "  Nothing  in  nature  is  more  certain  than 
that  the  function  of  bi-parental  reproduction  is  to 
produce  regressive  variation  ;  and  nothing  in  science 
is  more  remarkable  than  that,  in  spite  of  plain,  abun- 
dant, and  conclusive  evidence,  it  should  so  long  have 
been  regarded  as  the  cause  of  progressive  variations." 

Hence  it  appears  that,  in  every  species  which  is 
sexually  reproduced,  there  is,  on  the  average,  a 
greater  tendency  towards  reversion  than  towards 
progression,  a  greater  tendency  to  vary  towards  the 
ancestry  than  away  from  it ;  fur  the  weight  of  amphi- 
mixis is  always  thrown  upijn  the  side  of  regressive 
variations,  and  always  tends  towards  the  suppression 
of  progressive  variations.  Again,  to  quote  frum  Mr. 
Reid :  "  Under  conditions  of  natural  selection,  bi- 
parental  reproduction  ensures  that  all  [organic] 
evolution  shall  be  on  lines  of  small  variations,  not 
on  lines  of  great  abnormalities." 

Mr.  Reid  has  thought  this  matter  out  with  ex- 
treme completeness.  He  observes  that  bi-parental 
reproduction  occurs  invariably  in  all  large  and  com- 

1  The  word  type  in  biology  has  always  a  generalised  meaning, 
though  in  common  parlance  this  proper  meaning  of  the  term  is  fre- 
quently obscured. 


38  HEREDITY 

plex  organisms ;  that  is,  in  all  organisms  that  are 
apt  to  vary  uselessly  in  a  great  number  of  ways. 
Now  animals  are  more  complex  than  plants,  and 
therefore  have  a  greater  need  for  regressive  varia- 
tions. Hence  it  is  that,  while  plants  are  not  infre- 
quently self-fertilised,  animals,  save  in  a  very  few 
lowly  cases,  are  not.  He  concludes  his  remarkable 
chapter  by  saying  that  bi-parental  reproduction 
plays  exactly  the  same  part  in  selecting  regressive 
variations  that  natural  selection  plays  in  selecting 
progressive  variations.  Bi-parental  reproduction,  in- 
deed, is  only  another  name  for  bi-parental  selection. 
It  is  almost  as  important  a  fact  in  evolution  as 
natural  selection;  though  we  must  remember  that 
it  is  to  natural  selection  that  the  evolution  of  sex 
must  ultimately  be  referred. 

It  will  now  be  desirable  to  pass  from  the  methods 
recounted  in  this  chapter,  methods  mainly  of  actual 
observation  by  the  microscope  or  other  means,  to  a 
totally  different  point  of  view.  Thereafter,  perhaps, 
we  shall  be  able  to  see  that  some  conclusions  at  any 
rate  are  to  be  reached  by  widely  diverse  methods; 
and  this  will  constitute  a  high  presumption  in  their 
favour.  Only  after  the  reading  of  the  next  chapter 
can  we  safely  proceed  to  the  more  difficult  and 
important  part  of  our  subject. 


THE    BIOMETRIC    STUDY    OF    HEREDITY        ;iU 

CHAPTER    IV 

THE    BIOMETRIC    STUDY    OF    HEREDITY 

The  biometricians  are  a  comparatively  young  but 
very  important  school  of  biologists,  whose  founder 
is  Mr.  Francis  Galton,  Charles  Darwin's  first 
cousin,  and  whose  foremost  adherent  is  Professor 
Karl  Pearson,  to  whom  we  owe  the  term  biometry, 
or  biometrics.  The  characteristic  of  these  workers 
is  that  they  study  large  numbers  of  individuals,  or 
individual  characters ;  that  they  express  all  facts 
with  the  greatest  exactness  possible ;  that  they  con- 
sistently employ  mathematical  methods  in  all  their 
work ;  and  that  they  excel  in  the  detection  of 
fallacies.  Indeed  they  approach  biological  ques- 
tions with  a  unique  equipment  in  mathematics  and 
logic. 

A  large  number  of  conclusions  of  very  various 
kinds  already  stand  to  the  credit  of  the  biometri- 
cians. In  this  chapter  I  intend  to  note  the  more 
important  of  their  researches  which  bear  directly 
upon  the  problems  of  heredity  and  variation.  It  is, 
of  course,  a  fair  criticism  that  one  should  consider 
these  inquiries  each  in  strict  relation  to  the  subject 
of  which  it  treats ;  but,  on  the  other  hand,  the  dis- 
tinctive peculiarities  of  the  biometric  method  may 
be  held  to  justify  this  arrangement ;  and  tiie  reader 
will  lind  allusions  to  the  work  of  this  school  when- 
ever it  bears  directly  upon  the  various  subdivisions 
of  this  book.  It  is  necessary  to  remember  that  the 
science  of  heredity  is  yet  inchoate.     The  attempt  to 


40  HEREDITY 

reconcile  the  conclusions  of  every  school  of  workers 
would  therefore  be  not  only  futile,  but  premature. 
The  writer  is  thus  compelled  to  choose  some  mean 
between  the  impossible  ideal  of  presenting  a  com- 
plete account  of  an  incomplete  science  and  the 
very  unappetising  device  of  stating,  in  isolated  or 
mutually  contradictory  chapters,  the  conclusions  of 
all  the  different  groups  of  workers  in  this  field. 
The  biometricians,  however,  with  their  distinctive 
method  and  their  complete  independence  from  all 
save  mathematical  preconceptions,  do  very  definitely 
demand  this  kind  of  treatment. 

The  main  object  of  this  school  is  to  treat  the  pro- 
cesses of  evolution  quantitatively.  When  we  use 
terms  like  variation  and  selection,  the  biometricians 
demand  exact  measurement  of  them :  relative,  of 
course,  but  still  exact.  It  is  of  no  use  to  us,  they 
say,  to  be  told  that  an  organ  is  variable ;  we  must 
know  how  it  varies  in  a  thousand  individuals.  It  is 
of  no  use  to  tell  us  that  a  race  is  long-headed ;  we 
must  have  exact  measurements  of  the  cephalic  index 
in  a  thousand  individuals  of  that  race.  ...  Of  course 
it  is  obvious  that  a  very  large  number  of  biological 
statements  are  in  their  essence  statistical.  The  bio- 
metricians have  spent  much  labour  upon  the  critical 
examination  of  these  statements.  Indeed  it  may  be 
said  that  biometry  is  the  application  of  the  methods 
of  the  "higher  statistics"  to  biology.  Workers  in 
many  fields  are  beginning  to  discover  that  in  the 
absence  of  mathematical  training  they  are  hicom- 
petent  justly  to  appraise  any  of  their  statistical  or 
quantitative  results.  It  is  thus  a  most  satisfactory 
sicrn  of  the  times  that  medical  men,  for  instance, 


THE    BIOMETRIC    STUDY    OF    HEREDITY         41 

should  now  be  sending  their  observations  to  the 
biometricians  for  analysis  and  criticism.  The  readers 
of  the  British  Medical  Journal  have  greatly  profiled 
by  the  publication  therein  of  various  papers  by  Pro- 
fessor Karl  Pearson,  dealing  with  such  diverse  mat- 
ters as  the  inheritance  of  insanity  and  the  value  of 
anti-typhoid  inoculation.  It  is  now  becoming  evi- 
dent to  all  thoughtful  students  that  no  quantitative 
or  statistical  observations,  whether  dealing  with 
heredity  or  any  other  subject,  can  be  regarded  as 
complete  until  they  have  been  submitted  to  expert 
mathematical  criticism.  There  is  no  questioning  the 
dictum  of  Kant,  that  the  completeness  and  validity 
of  any  objective  science  is  proportioned  to  the  degree 
in  which  it  is  informed  with  mathematics.  Some- 
times, when  the  student  wants  a  laugh,  he  tries  to 
picture  the  results  of  submitting  the  crude  and  ludi- 
crous arguments  for  and  against  "  Fiscal  Reform,"  to 
the  criticism  of  the  mathematician.  But  "let  that 
pass." 

Ignoring  for  the  nonce  the  critical  and  corrective 
services  of  biometry,  we  may  note  the  chief  of  those 
constructive  efforts  which  already  stand  to  the  per- 
manent credit  of  its  youth.  The  tirst  of  these  is  now 
known  as  "  Galton's  Law."  Many  years  ago  Mr. 
Galton  devoted  himself  to  the  exact  study  of  "human 
faculty  "  in  relation  to  heredity ;  and  also  to  the  study 
of  the  inheritance  of  physical  characters  in  certain  of 
the  lower  animals.  He  collected  and  analysed  an 
enormous  number  of  data  as  to  health,  eye-colour, 
stature,  and  artistic  faculty  in  several  generations  of 
some  hundred  and  (ifty  distinct  famihes.  Later  he 
was  able  to  study  the  records  of  the  colours  of  a 


42  HEREDITY 

large  pedigree  stock  of  Basset  hounds  (dwarf  blood- 
hounds) belonging  to  Sir  Everett  Millais.  He  found 
that  the  human  and  canine  data,  widely  various  as  they 
were,  could  yet  be  expressed  in  an  exceedingly  simple 
generalisation  which  he  called  the  law  of  ancestral 
inheritance.  In  all  probability  this  law  may  prove 
to  be  universally  true  of  bi-parental  reproduction. 
There  is  a  quite  valid  sense  in  which  we  regard 
inheritance  as  dual,  half- paternal,  half- maternal. 
But  it  is  plain  that  the  same  applies  to  the  inherit- 
ance of  each  parent,  and  so  on  ad  infinitnin.  Hence 
the  inheritance  of  each  individual  is  not  dual  but 
multiple,  and  Mr.  Galton  has  proved  that  it  is 
actually  capable  of  exact  mathematical  expression. 
But  before  we  see  what  this  is  it  is  necessary  to  state, 
as  clearly  as  may  be,  that  Galton's  Law  deals  with 
races  and  generations,  not  with  individuals.  In  the 
discussion  of  the  principles  of  heredity,  or  indeed  of 
any  biological  generalisation,  it  seems  impossible  to 
bring  home  to  some  people  the  idea  that  they  are 
generalisations,  710^  "  particularisations."  The  objec- 
tions of  such  people  imply  a  confusion  of  thought 
such  as  that  which  would  suppose  the  statement  of 
a  cricketer's  batting  average  as  twenty  to  mean  that 
whenever  he  went  to  the  wickets  he  made  twenty 
runs,  never  more,  never  less.  The  law  about  to  be 
stated  is  an  average,  and  much  less  to  be  disproved 
by  the  quotation  of  single  instances  than  the  state- 
ment of  the  batsman's  average  is  disproved  by  the 
observation  that  on  such  and  such  an  occasion  he 
made  a  "  duck  "  or  a  "  century." 

Galton's   Law   may   thus   be   stated  : — "  The   two 
parents    between    them   contribute   on  the    average 


THE    BIOMETRIC    STUDY    OF    HEREDITY         43 

one-half  of  each  inherited  faculty  [or  character], 
each  of  them  contributing  one-quarter  of  it.  The 
four  grandparents  contribute  between  them  one- 
quarter,  or  each  of  them  one-sixteenth,  and  so  on, 
the  sum  of  the  series,  i  +  i  +  i  +  iV  +  ^^c.,  being 
equal  to  one,  as  it  should  be.  It  is  a  property  of  this 
infinite  series  that  each  term  is  equal  to  the  sum  of 
all  those  that  follow."  The  opinion  of  Professor  Karl 
Pearson,  in  which  there  concurs  a  biologist  of  so 
different  a  school  as  that  to  which  Professor  J.  A. 
Thomson  belongs,  is  that  Galton's  Law  expresses  in 
one  simple  generalisation  the  ultimate  result  of  all 
the  complex  factors  in  heredity. 

Certain  comments  fall  to  be  made  upon  this  law. 
We  have  already  seen  that,  in  accordance  with 
Weismann's  conception  of  the  "  continuity  of  the 
germ-plasm,"  the  line  of  descent  is  not  really  from 
individual  to  individual,  but  from  germ-cell  to  germ- 
cell.  Plainly,  however,  Galton's  Law  deals  with  indi- 
viduals. But  Mr.  Galton  has  himself  pointed  out 
that  the  independent  establishment  of  this  law  by  no 
means  involves  the  rejection  of  Weismann's  concep- 
tion. On  the  contrary,  the  two  are  compatible  and 
complementary.  For  though  Galton's  Law  deals 
ostensibly  with  individuals,  we  now  know  enough  nf 
the  origin  of  the  individual  to  see  that  it  may  always 
be  taken  as  fairly  representative  of  its  own  gurm- 
cells,  to  which,  indeed,  its  relation  is  not  parental  but 
fraternal;  for  the  one  primal  cell  may  be  conceived 
as  giving  rise  by  its  divisions  on  the  one  hand  to  the 
individual,  and  on  the  other  to  his  germ-cells.  J^iit 
even  more  signiticant  is  the  manner  in  which  Galton's 
Law  corresponds  with  the  observed  facts  of  nuclear 


44  HEREDITY 

change  prior  to  the  union  of  the  male  and  female 
gametes.  For  we  have  seen  that  one-half  of  the 
nuclear  chromatin  of  each  gamete  is  thrown  aside 
prior  to  the  fusion  of  the  two  nuclei.  This  obviously 
corresponds  exactly  with  Galton's  assertion  that  the 
two  parents  between  them  contribute  one-half  of  the 
total  heritage  of  the  offspring.  Thus  the  facts  of 
nuclear  change  in  the  process  of  gametogenesis  (i.e. 
the  formation  of  the  gametes  from  their  mother-cells) 
as  observed  by  the  microscope  in  the  case  of  various 
very  simple  animals,  precisely  correspond  with  a 
mathematical  formula  derived  by  Mr.  Galton  from 
the  study  of  the  inheritance  in  man  of  such  things  as 
"artistic  faculty."  Surely  we  are  entitled  to  regard 
Galton's  Law  as  demonstrably  true. 

Its  importance  can  scarcely  be  overestimated.  It 
is  the  theoretical  basis  upon  which  Galton  and 
Pearson  have  constructed  a  whole  series  of  important 
conceptions  that  have  already  served  the  science  of 
heredity.  It  has  been  shown  to  be  more  comprehen- 
sively true  than  even  its  discoverer  recognised.  It  is 
even  found  to  survive  the  criticism  passed  upon  it  by 
the  recent  experimental  study  of  variation  in  plants 
and  other  organisms.  But  whilst  we  freely  recog- 
nise the  importance  and  value  of  this  law  and 
its  elaborations,  we  must  not  delude  ourselves  with 
the  idea  that  it  leaves  nothing  to  explain.  In  a 
certain  sense,  perhaps,  Galton's  Law,  as  extended  by 
Pearson,  may  be  said  to  "  render  the  whole  theory 
of  heredity  simple,  straightforward,  and  luminous  "  ; 
but  it  is  evident  that  the  author  of  this  opinion  was, 
for  the  moment,  taking  a  very  narrow  view  of  the 
problems  involved  in  the  means  by  which  Galton's 


THE    BIOMETRIC    STUDY    OF    TTEREniTV        45 

Law  works  itself  out.  Nevertheless  we  must  admit 
that,  from  the  special  standpoint  of  the  biometrician, 
this  law  must  appear  to  be  all  that  Dr.  Vernon 
thinks  it. 

Most  valuable  results  have  followed  the  work  of 
the  bionietricians  upon  the  variableness  of  such  struc- 
tures as  leaves,  hairs,  or  scales,  which  are  repeated 
in  the  bodv  of  the  same  individual  orijanism.  With- 
out  detailing  the  highly  complex  methods  employed 
in  this  study,  and  without  noting  certain  tentative 
results  which  may  prove  to  be  of  great  value,  we 
may  pass  at  once  to  the  bearing  of  these  studies 
upon  the  facts  of  bi-parental  reproduction.  The 
reproductive  cells  must  be  regarded  as  "  serial  homo- 
logues,"  the  name  applied  to  structures  repeated  in 
the  body  of  one  individual.  Now  the  comparative 
study  of  brothers  is  plainly  a  means  by  which  we  can 
study  the  variableness  of  the  reproductive  cells  of 
the  father.  But  in  the  study  of  the  production  by  a 
man  of  repeated  sex-cells,  represented  by  his  sons, 
there  is  the  obvious  complication  that  the  sons  are 
derived  from  their  mother  as  well :  the  case  is  hardly 
parallel  to  that  of  the  repetition  of  leaves  (which  are 
not  sexually  produced,  of  course)  on  the  body  of  a 
plant.  But  Pearson  has  made  the  very  important 
observation  that  the  variableness  of  human  children 
"  obeys  the  same  law  as  that  of  other  repeated  struc- 
tures." These  biometric  observations  are  of  great 
value  in  enabling  us  to  reject  Weismann's  theory  of 
the  function  of  bi-parental  reproduction  as  a  cause 
of  variations  :  for  they  unquestionably  show  that  no 
increase  of  variableness  is  associated  with  this 
method  of  reproduction.     Let  us  clearly  understand 


46  HEREDITY 

the  argument.  Sex-cells  and  leaves  (for  instance) 
are  structures  repeated  in  the  same  individual.  We 
measure  the  variableness  of  the  leaves,  and  then 
that,  not  of  the  sex-cells,  indeed,  but  of  sexually  pro- 
duced children — whose  variableness  represents  that 
of  the  father's  sex-cells  plus  so  much  variableness  as 
may  be  due  to  the  fact  that  each  child  is  the  product 
not  of  the  paternal  sex-cell  only,  but  of  that  and 
another.  But  it  is  found  that  the  correlation  between 
the  children  thus  produced  is  no  less  than  that 
between  leaves  repeated  on  one  individual  plant. 
Plainly,  therefore,  the  occurrence  of  bi-parental 
reproduction  has  not  been  a  cause  of  variation. 

Lastly,  we  may  note  one  of  the  very  latest  results 
gained  by  the  methods  of  biometry.  The  relative 
variability  of  man  and  woman  has  long  been  dis- 
cussed. Some,  regarding  the  matter  from  the  phy- 
sical side,  have  believed  that  woman  is  more  variable 
than  man.  Others,  considering  the  mental  characters 
of  the  two  sexes,  have  declared  that  woman  is  more 
conservative,  that  is  to  say,  less  variable,  than  man. 
It  is  man,  they  say,  who  always  originates  the  new 
ways  of  thinking,  which,  in  any  sphere,  are  first 
stigmatised  as  heresy.  Heresy,  of  course,  is  none 
other  than  variation  in  the  realm  of  thought,  and  is 
as  necessary  to  progress  in  the  realm  of  ideas  as 
physical  variation  in  the  realm  of  anatomy. 

But  the  biometricians  have  clearly  shown — con- 
fining themselves,  as  one  might  expect,  to  the  phy- 
sical side  of  the  question — that  no  difference  between 
the  variability  of  man  and  woman  can  be  detected. 
It  might  indeed  have  been  anticipated  a  priori  that 
no  correlation  between  sex  and  variability  would  be 


THE    FACTS    AND    LAWS    OF    VAKTATTOy        47 

discovered.  For,  whatever  be  said  to  the  contrary, 
the  two  sexes,  from  the  biological  point  of  view,  arc 
strictly  equal  and  complementary. 


CHAPTER    V 

THE    FACTS    AND    LAWS    OF    VARIATION 

A  CHAPTER  is  formally  devoted  to  this  subject  simply 
for  the  sake  of  emphasis.  The  reader  has  already 
seen  that  in  discussion  of  strict  correlatives,  such  as 
heredity  and  variation,  the  two  cannot  be  dissociated, 
since  each  implies  the  other.  Thus  in  the  preceding 
and  following  chapters  we  find  as  much  to  say  of 
variation  as  of  heredity.  But  the  emphasis  of  a 
separate  chapter  may  be  of  use  in  enabling  us  fully 
to  appreciate  the  conclusion  which  has  been  reached 
by  the  a  loosteriori  study  of  variation. 

We  have  already  argued  that  certain  current  ways 
of  looking  at  variation  are  untenable.  Not  concern- 
ing ourselves  with  the  detailed  facts  that  may  be 
observed,  we  have  argued  deductively  from  certain 
principles  that  variations  cannot  be  regarded  as 
arbitrary  or  as  outside  the  law  of  causation,  or  as 
incalculable  or  as  accidental  lapses  on  the  part  of  the 
law  of  heredity,  and  that,  as  believers  in  the  Uni- 
formity of  Nature,  we  must  hold  to  our  view  in  spite 
of  appearances. 

But  the  fact  here  to  be  insisted  upon  is  that 
"  appearances  "  are  for  us  and  not  against  us.  We 
find  that  when  we  come  systematically  to  study  the 
facts  of  variation,  they  are  not  arbitrary  or  incalcul- 


48  HEREDITY 

able.  We  find,  on  the  contrary,  as  has  been  illus- 
trated in  the  previous  chapter,  that  these  facts, 
though  admittedly  incalculable  for  the  individual, 
are  yet  capable  of  mathematical  expression,  often  of 
the  simplest,  when  we  consider  large  numbers  of 
individuals.  Similarly  the  physicist,  be  he  a  Kelvin, 
is  unable  precisely  to  predict  the  size  and  course  of 
all  the  fragments  produced  by  an  explosion.  Yet  he 
knows  that  the  laws  of  motion  and  gravitation  and 
chemical  combination  and  gaseous  pressure  are  ob- 
served, and  his  knowledge  is  not  affected  by  the 
circumstance  that  his  limited  powers  do  not  suffice 
for  precise  prediction  in  such  a  case ;  nor  would  he 
regard  with  anything  but  sympathy  the  writer  who 
should  say,  "Well,  I  am  content  to  conclude  that, 
since  no  one  can  predict  the  course  and  weight  of 
even  one  of  these  fragments,  either  there  are  no  laws 
in  the  matter,  or  else  they  are  wholly  unknown." 
This  is  precisely  what  is  said  by  the  critics  in  relation 
to  the  study  of  such  subjects  as  variation;  and  the 
criticism  is  as  worthless  in  one  case  as  in  the  other. 
When  variation  is  studied  on  a  sufficiently  ample 
scale — in  accordance  with  the  general  principles  of  a 
'posteriori  reasoning,  for  the  more  numerous  the 
foundation-facts,  the  more  secure  and  comprehen- 
sive must  be  the  generalisation  erected  upon  them — 
we  find  the  facts  are  capable  of  being  expressed  in 
certain  general  propositions,  such  as  are  commonly 
called  laws  in  scientific  writings. 

There  is  a  fundamental  distinction  between  a  law 
and  a  cause,  as  the  case  of  gravitation  suffices  to 
illustrate.  Nevertheless,  we  are  surely  entitled  to 
assume  that  the  occurrence  of  a  law,  i.e.  of  a  natural 


THE   FACTS    AND    LAWS    OF    VARIATION        49 

order,  implies  a  natural  cause.  In  point  of  fact, 
we  all  do  make  this  assumption.  We  do  not  pray 
that  two  days  shall  follow  one  another  without  an 
intervening  night,  for  the  invariable  sequence  of 
night  and  day  has  caused  us  to  assume  that  it  lies 
within  the  sphere  of  natural  causation.  Similarly 
the  "  Book  of  Common  Prayer  "  still  contains  a  form 
of  prayer  for  rain,  meteorology  not  being  sufficientl}' 
advanced  to  enunciate  such  laws  as  would  convince 
unthinking  men  that  the  weather,  also,  is  determined 
by  natural  causation. 

Now,  in  the  case  of  variation,  it  may  similarly 
be  argued  from  the  existence  of  the  laws  which  the 
Mendelians,  the  biometricians,  and  others  have 
discovered  that  this  phenomenon,  like  all  others, 
is  within  the  sphere  of  natural  causation.  It  is, 
then,  submitted  that  a  priori  considerations  and  a 
posteriori  considerations  (viz.  the  fact  that  it  is  pos- 
sible to  enunciate  laws  of  variation),  lead  alike  to  the 
same  conclusion,  that  the  causes  of  variation  are  to 
be  found  in  the  natural  order  of  thini^^s.  So  certain 
is  the  evidence  of  these  complementary  lines  of 
reasoning  that  our  faith  in  their  common  conclusion 
is  not  shaken  by  the  circumstance  that,  as  we  shall 
see,  the  causes  of  variation  are  still  somewhat 
obscure. 

CHAPTER   VI 
THE   ORIGIN   OF   VARIATIONS 

It  is  of  the  first  importance  that  we  should  have 
an  understanding  of  the  causes  that  produce 
variation.     It  is  so,  not  merely    by    reason   of   the 


50  HEREDITY 

frequency  of  variation,  or  the  fact  that  it  so  con- 
stantly accompanies  heredity,  but  pre-eminently 
because  of  the  supremely  important  role  of  varia- 
tions. As  Bateson  says  of  heredity  and  variation : 
"  Every  one  knows  that,  somewhere  hidden  among 
the  phenomena  denoted  by  these  terms,  there  must 
be  principles  which,  in  ways  untraced,  are  ordering 
the  destinies  of  living  beings."  Without  variations, 
natural  selection  would  have  no  material  upon 
which  to  work.  Even  when  we  limit  the  term,  as  is 
done  throughout  these  chapters,  to  mean  what  are 
sometimes  distinguished  as  blastogenic  variations, 
those  true  variations  which  have  their  seat  in  the 
germ,  we  must  recognise  that  without  variation  there 
could  be  no  evolution. 

What,  then,  is  the  origin  of  true  variations : 
"  spontaneous  "  or  "  germinal "  or  "  blastogenic  " 
variations  ? 

We  are  long  past  the  days  when  it  was  possible 
to  speak  of  heredity  and  variation  as  opposing 
"  forces  "  or  "  principles."  These  are  good  words 
in  their  place  ;  out  of  their  place  they  merely  cloak 
ignorance.  Also,  we  cannot  be  satisfied  by  explaining 
variation  in  accordance  with  that  amusing  piece  of 
nonsense  known  as  the  Bathmic  ^  theory  of  organic 
evolution,  which  attributes  it  to  an  "  inherent  adap- 
tive growth-force."  Nor  have  we  any  use  to-day 
for  the  hypothesis  that  variations  are  unique 
amongst  phenomena  in  being  outside  the  law  of 
universal  causation ;  that  they  are  directly  due  to 
the  designing  volition  of  a  Divine  Person.  If  all 
rational  explanations  fail  us,  we  must  not  content 

1  From  the  Greek  bathmis,  a  step. 


THE    ORIGIN    OF    VARIATIOXS  .51 

ourselves  with  the  adoption  of  vague  but  imposing 
phrases,  nor  seek  to  darken  counsel  by  words  without 
knowledge. 

In  the  case  of  the  lowliest  organisms,  such  as, 
for  example,  the  animal  Ama'ba,  or  the  vegetable 
bacterium,  we  can  draw  no  distinction  between  the 
germ-plasm  and  the  body-plasm.  Any  acquire- 
ment, such  as  the  exahation  of  virulence  due  to  the 
passage  of  disease -producing  bacteria  through  the 
body  of  a  susceptible  animal,  must  be  a  cause  of 
variation ;  for  the  descendants  of  such  bacteria  are 
certainly  more  virulent  than  were  their  ancestors 
before  their  experience  of  this  suitable  environment. 

But  the  problem  before  us  is  the  origin  of  varia- 
tions in  all  the  higher  animals  and  plants,  which 
are  propagated  by  bi-parental  reproduction. 

In  the  first  place,  we  find  ourselves  compelled  to 
reject  certain  suggested  causes  of  variation  in  these 
organisms.  We  find  that,  even  assuming  the  acquire- 
ments of  the  individual  so  to  alter  the  germ-plasm 
on  occasion  as  to  produce  true  variations,  yet  this 
transmission  of  acquirements  is  totally  inadequate 
to  explain  the  great  majority  of  cases  of  variation. 

Even  the  most  recent  opinion  of  Weismann  (which 
is  in  some  measure  a  concession  to  his  critics),  that 
the  germ-plasm,  on  rare  occasions  and  to  a  small 
extent,  may  be  so  affected  by  its  surroundings  as  to 
give  rise  to  variations  in  the  ofispring,  is  almost 
infinitely  far  from  being  tantamount  to  au  adequate 
explanation  of  the  cause  of  variations. 

We  find,  again,  that  it  is  impossible  to  explain 
variation  by  the  assumption  of  a  direct  action  of  the 
external   environment   (by   which    clumsy  phrase   I 


52  HEREDITY 

mean  the  environment  other  than  the  individual 
body)  upon  the  germ -plasm,  such  an  assumption 
being  unsupported  by  evidence. 

Yet  a  third  suggestion,  as  we  have  seen,  must  be 
rejected  in  consequence  of  the  work  of  the  last 
decade.  We  must  reject  as  incompatible  with  the 
facts  the  theory  of  Weismann  that  the  great  cause  of 
variations  is  amphimixis  or  bi-parental  reproduction. 
We  must  reject  this  theory  despite  its  apparent 
adequacy  and  its  attractiveness,  and  despite  the  fact 
that,  having  rejected  it,  we  are  almost  at  our  wits' 
end  for  a  better. 

Let  us  see  how  the  difficulty  is  met  by  Archdall 
Reid,  after  his  brilliant  exposition  of  the  evidence 
which  has  led  to  the  rejection  of  Weismann's  theory. 
He  declares  that  spontaneous  variations  are  due 
"undoubtedly  to  an  inborn  tendency  to  vary,  a 
tendency  that  is  inherent  in  the  germ-plasm  of  every 
species  of  plant  and  animal."  Certainly  Mr.  Reid 
does  not  offer  this  answer  without  an  attempt  to 
explain  the  origin  and  cause  of  this  tendency,  but 
after  the  most  careful  study  of  his  speculations, ^  I 
confess  that  they  afford  me  no  satisfaction,  and  I 
cannot  persuade  myself  that  they  are  worth  quoting. 
When  we  come  to  the  summary  of  the  first  section  of 
his  work,  we  read  : — 

"  IV.  A  progressive  variation  constitutes  a  deviation 
from  the  parental  and  ancestral  type,  which,  speaking 
generally,  is  in  the  direction  of  increased  magnitude  and 
complexity.  It  results  from  the  complete  recapitulation 
of  the  parental  development  plus  an  addition." 


1  «' 


Principles  of  Heredity,"  p.  95. 


THE    ORIGIN    OF    VAKIATIONS  5.'5 

Which  raises  the  natural  c|iiery — Whence  the  addi- 
tion ?  The  addition  is  the  essence  of  the  variation ; 
it  is  the  variation.  Hence  the  last  sentence  quoted, 
which  professes  to  exphxin  the  cause  of  the  variation, 
does  not  seem  to  nie  to  fulfil  its  promise.  Surely 
when  Mr.  Reid  wrote  "  It  results  from  .  .  .  ."  he 
meant  "  It  consists  in  .  .  .  ." 

If  next  we  consult  the  admirable  arti(;le  on  heredity 
recently  contributed  by  Professor  Arthur  Thomson  to 
the  Encyclopaedia  Medica,  we  find  no  discussion  of 
the  cause  of  variations,  save  in  so  far  as  his  cautious 
rejection  of  the  doctrine  that  acquirements  are 
transmitted  {i.e.  are  causes  of  variation)  answers  to 
this  description. 

Next  we  may  hopefully  turn  to  the  article,  "Varia- 
tion and  Selection,"  recently  written  by  Professor 
Weldon  for  the  new  volumes  of  the  Encyclopedia 
Britannica.  But  again  we  are  disappointed.  True, 
Professor  Weldon  cites  the  evidence  which  disproves 
Weismann's  theory  that  bi-parental  reproduction  is 
the  chief  cause  of  variations ;  but  the  only  positive 
statement  as  to  the  true  cause  of  variation  is  that, 
"  the  production  of  a  regular  series  of  variations, 
under  given  environmental  conditions,  is  a  property 
of  species  as  constant  as  the  production  of  typical 
individuals."  This  is  an  exceedingly  important 
proposition,  but  it  does  not  satisfy  us  who  are  scek- 
iuLT  to  know  the  cause  or  causes  of  variations.  The 
author  of  the  new  article,  "Embryology,"  in  the  same 
work,  who  is  no  less  a  person  than  Hans  Driesch, 
inclines  to  the  theory  of  Weismann.  Dr.  Chalmers 
Mitchell,  the  author  of  the  new  article,  "  Evolu- 
tion,"   clearly    recognises    the     distinction    between 


54  HEREDITY 

formulating  laws  of  variation  and  explaining  the 
causes  of  variation,  but  he  gives  us  no  further 
help. 

Let  us  now  return  to  Weismann  himself,  and  see 
whether  he  has  any  further  light  to  throw  on  our 
problem  besides  that  which  we  have  already  rejected 
— the  statement  that  true  variations  are  due  to 
amphimixis.  Weismann's  theory  of  the  continuity 
of  the  germ-plasm  was  first  advanced  in  1883.  Ten 
years  later,  in  his  work,  "  The  Germ-Plasm,"  Weis- 
mann explained  true  variations  as  due  to  the  direct 
action  of  external  influences  upon  the  hypothetical 
"  biophors  "  and  "  determinants  "  of  the  germ-plasm. 
The  relation  between  the  germ-plasm  and  their 
environment  is  nutritive,  as  we  shall  see  in  discussing 
the  possibilities  of  modification  of  the  germ-plasm 
by  the  body  of  the  individual.^  Weismann  supposes 
the  constituent  structures  of  the  germ -plasm  to 
undergo  incessant  changes  of  composition  during 
their  residence  in  the  body  of  the  individual,  and 
these  changes  are  the  essential  causes  of  variation. 
The  immediate  cause  of  these  changes  is  to  be  found 
in  the  "  inequalities  of  nutrition  "  to  which  the  deter- 
minants are  subject.  Thus  though  it  is  amphimixis^ 
that  Weismann  regards  as  causing  the  constant 
occurrence  of  variations  as  seen  in  the  individual, 
he  inclines  to  the  view  that  amphimixis  is  not  the 
primary   cause   of  these  variations,   "but   that   the 

1  Chapter  X. 

2  Amphimixis  is  the  term  applied  not  only  to  the  union  of  the 
male  and  female  nuclei  in  bi- parental  reproduction,  but  also  to  the 
conjugation  or  union  of  two  entire  individuals,  often  observed  in 
unicellular  organisms. 


THE    ORIGIN    OF    VARIATIONS  55 

process  furnishes  an  inexhaustible  supply  of  fresh 
combinations  of  individual  variations."  ^ 

We  owe  to  Dr.  Vernon  a  recent  and  careful  con- 
sideration of  the  evidence  in  favour  of  these  two 
factors.  Amphimixis  we  have  ah'eady  rejected  as  a 
cause  of  progressive  variations — variations  away  from 
the  specitic  type — though  it  may  be  a  cause  of  re- 
gressive variations — back  to  the  type.  Dr.  Vernon, 
however,  accepts  the  teaching  of  Weismann  on  this 
point,  but  it  is  probably  not  necessary  here  to  re- 
consider the  evidence  which  he  advances. 

It  is  of  importance,  however,  carefully  to  consider 
the  evidence  in  favour  of  the  view  that  the  ultimate 
cause  of  variations  is  to  be  found  in  inequalities  of 
nutrition  acting  on  the  individual  constituents  of  the 
germ-plasm.  Dr.  Vernon  conducted  a  long  series  of 
experiments  on  the  sex-cells  of  the  sea-urchin,  known 
to  systematists  as  Strongylo-centrotus  lividus.  The 
ova,  or  the  spermatozoa,  or  both,  were  kept  for 
varying  numbers  of  hours  in  sea-water  before  fertili- 
sation was  allowed  to  occur ;  and  after  eight  days  the 
larvae  resultiui^f  from  the  fertilisation  were  measured. 
It  was  found,  in  brief,  that  differences  in  the  degree 
of  freshness  of  these  gametes,  that  is  to  say,  "in- 
equalities of  nutrition  acting  on  the  germ-plasm," 
had  "  a  very  appreciable  effect  upon  the  size  of  the 
subsequently  developing  larva\"  The  efiects  differed 
markedly  according  as  whether  the  female  or  the 
male  gametes,  or  both,  were  stale  or  fresh  ;  whence  it 
may  be  inferred  that  different  portions  of  the  same 
sex-cell  may  also  react  differently  to  one  and  the 

1  I  quote  from  the  excellent  chapter,  "  Blastogeinc  Variulions," 
in  Dr.  H.  M.  Vernon's  "  Variations  in  Animals  and  Plants."  (Inter- 
national Scientific  Series,  vol.  Ixxxviii.) 


56  HEREDITY 

same  change  of  nutrition.  The  difference  between 
male  and  female  gametes  is  presumably  a  difference 
of  determinants,  hence  the  difference  in  the  reaction 
of  the  male  and  female  gametes  is  a  difference  of 
reaction,  not  on  the  part  of  the  cells  as  a  whole,  but 
on  the  part  of  certain  of  their  determinants — which  is 
precisely  in  accordance  with  Weismann's  contention. 
Other  experiments  demonstrated  the  existence  of  a 
seasonal  variation,  showing  that  "  inequalities  of 
nutrition"  dependent  on  the  time  of  year  un- 
doubtedly affect  the  sex-cells  of  the  sea-urchin, 
which  are  typical  of  germ-plasm  in  general. 

Various  experiments  of  Cossar  Ewart  on  the  rabbit, 
and  of  De  Vries  on  plants,  seem  also  to  support  the 
view  that  the  germ-plasm  is  affected  by  "inequali- 
ties of  nutrition."  But,  indeed,  the  assertion  that 
the  germ-plasm,  unlike  all  other  living  entities,  is 
not  subject  to  change  in  virtue  of  its  converse  with 
its  environment,  was  quite  incredible  from  the  first. 

But,  since  we  are  consulting  authorities,  we  will 
do  well  to  consider  the  conclusions  reached  by  the 
profoundest  intellect — not  even  excepting  Aristotle's 
— that  has  ever  been  applied  to  the  problems  of 
biology.  In  his  "  Principles  of  Biology,"  published 
forty  years  ago,  Herbert  Spencer  considered  the 
question  of  the  origin  of  variations,  and  it  goes 
without  saying  that  he  did  not  content  himself 
with  any  such  petitio  ponncipii  as  is  involved  in 
the  assumption  of  an  "inherent  tendency  to  vary." 
Spencer's  discussion  of  the  question  follows  closely 
upon  his  setting  forth  of  the  great  conception  of 
"  physiological   units,"   which    now — under    various 


THE    ORIGIN    OF    VARIATIONS  57 

aliases — plays  a  leading  part  in  all  theories  of 
heredity  and  variation.  This  conception,  combined 
with  certain  of  the  abstract  conclusions  reached  in 
"First  Principles,"  enables  Spencer  to  account  for 
the  "spontaneous  variation"  of  new  individuals 
simultaneously  produced  by  the  same  parent — ani- 
mals of  the  same  litter.  Plainly  this  is  the  case 
which  most  severely  tests  any  proti'ered  explanation 
of  the  causes  of  variation. 

Now  Spencer  had  already  enunciated  a  law  termed 
by  him  the  law  of  the  instability  of  the  homogeneous. 
In  ordinary  language  this  law  may  be  interpreted 
as  stating  that  any  homogeneous  aggregate  neces- 
sarily tends  to  become  heterogeneous,  since  its 
several  (similar)  parts  are  necessarily  exposed  to 
different  forces,  and  are  therefore  of  necessity  differ- 
ently modified.  Spencer  illustrates  this  law  from 
astronomy,  geology,  sociology,  biology,  and  psycho- 
logy. Now,  if  we  apply  the  law  of  the  instability 
of  the  homogeneous  to  the  mother-germ-cell,  which, 
by  the  process  called  gametogenesis — the  genesis  of 
gametes — divides  and  gives  rise  to  the  actual  gametes, 
or  sex-cells,  we  see  that,  since  no  two  parts  of  any 
aggregate  are  subject  to  precisely  the  same  forces, 
and  must  therefore  become  dissimilar,  no  two  ova, 
spermatozoa,  or  pollen-cells,  formed  as  they  are  by 
a  process  of  evolution  from  the  mother-germ-cell, 
can  he  identical.  Between  them  there  must  be 
"small  initial  differences  in  the  proportions  and 
condition  of  the  slightly  unlike  physiological  units." 
At  once  we  see  that  the  view  of  Weismann  had  been 
anticipated.  The  "small  initial  differences"  in  the 
"physiological  units" — or  "determinants" — arise  in 


58  HEREDITY 

consequence  of  the  fact  that  no  two  parts  {e.g.  physio- 
logical units  or  determinants)  of  the  mother-germ- 
cell  were  subject  to  precisely  the  same  forces.  This 
plainly  recalls  the  Weismannian  explanation — "  in- 
equalities of  nutrition." 

Thus  we  are  prepared  to  understand  that  the 
essence  of  variation  is  a  novelty  in  the  cell-divisions, 
by  which  the  mother-germ-cell,  or  germ-mother-cell, 
gives  rise  to  the  "germ-daughter-cells,"  and  these 
to  the  "germ-granddaughter-cells,"  which  are  the 
gametes,  or  germ-cells,  themselves.  This  novelty  is 
a  deduction,  in  the  pages  of  Spencer,  from  the  law 
of  the  instability  of  the  homogeneous.  Forty  years 
later  we  find  Professor  Bateson  saying,  in  a  Presiden- 
tial Address  to  the  Zoological  section  of  the  British 
Association  (1904),  that  "  variation  is  a  novel  cell- 
division  " :  that  is,  a  novel  cell-division  during  the 
process  of  gametogenesis.  Bateson's  assertion  did 
not  depend  on  the  validity  of  Spencer's  deduction 
of  1864,  but  was  based  upon  the  work  of  the  Abbe 
Mendel  and  his  recent  followers — work  which  we 
shall  consider  in  the  next  chapter. 

But  even  now  we  have  not  yet  adduced  all  the 
reasons  for  looking  up  the  pages  of  Spencer  before 
passing  to  the  consideration  of  Mendelism.  For 
Spencer  goes  on  to  say,  in  the  paragraph  from  which 
I  have  already  quoted,^  that  another  fact  in  the  link 
of  events  which  determines  variation  is  the  "  segre- 
gation which  inevitably  goes  on  in  any  mixed  aggre- 
gate of  units  and  prevents  a  homogeneous  mean 
between  the  two  parents."  The  existence  of  this 
segregation    in    the    case    under    consideration    is 

1  "Principles  of  Biology,"  §  88. 


THE    ORIGIN    OF    VARIATIONS  .50 

deduced  by  Spencer  from  his  general  conclusion, 
reached  in  §  163  of  "  First  Principles,"  that  there 
must  always  be  a  process  of  segregation,  since  evolu- 
tion consists  in  a  change  from  the  homogeneous,  not 
to  a  "  vague  chaotic  heterogeneity,"  but  to  an  orderly 
heterogeneity.  The  terminology  is  somewhat  difH- 
cult  to  those  unfamiliar  with  it,  but  the  reader  is 
merely  asked  to  note  Spencer's  arrival  by  deduction 
— i.e.  reasoning  from  the  general  to  the  particular — 
at  the  conclusion  that  segregation  plays  a  part  in 
variation,  ensuring  that  variation — which  is  only  a 
special  case  of  universal  evolution — is  orderly  and 
not  chaotic ;  and  that,  in  the  case  wo  are  considering, 
it  "  prevents  a  homogeneous  mean  between  the  two 
parents."  In  the  next  chapter  we  shall  see  how  the 
Abbe  Mendel  reached  similar  conclusions  as  to  the 
nature  of  variations  by  the  opposite  method  to 
Spencer's,  by  induction — i.e.  reasoning  from  the 
particular  to  the  general — from  the  experimental 
facts  which  he  had  observed.  It  is  not  a  little 
remarkable  that  Spencer's  a  priori  reasoning,  and 
Mendel's  a  posteriori  reasoning,  should  have  coin- 
cided in  time.  It  is  quite  probable  that  on  the  very 
day  when  Spencer  wrote  the  paragraphs  I  have 
quoted,  Mendel  had  conducted  experiments  on  peas ; 
yet  we  may  be  almost  certain  that  neither  of  them 
had  ever  heard  the  other's  name :  and  science  was  to 
wait  several  decades  before  the  work  of  the  experi- 
menter was  to  be  brought  into  correlation  with  the 
conclusions  of  the  philosopher. 


60  HEREDITY 

CHAPTER    VII 
MENDELISM 

As  is  asserted  at  length  in  another  volume,^  the 
theory  of  organic  evolution  was  re-stated  by  Darwin 
in  1859,  in  a  form  which  has  stood  the  test  of  the 
most  intellectually  active  decades  in  history.  Dar- 
win took  for  granted  the  existence  of  variations,  and 
showed  how  animal  and  vegetable  species  might 
have  their  origin  in  the  selection  of  such  variations 
as  were  advantageous  in  the  struggle  for  existence. 
This  theory  of  natural  selection  is  now  a  truth  ques- 
tioned by  no  competent  and  very  few  incompetent 
critics.  This  granted,  it  is  seen  to  be  a  matter  of 
prime  importance  for  evolutionary  theory,  as  we 
have  already  observed,  that  we  should  determine 
the  causes  of  variation,  and  formulate  the  laws  of 
variation — if  such  there  be — as  no  man  of  science 
can  doubt.  But  during  nearly  all  these  past  years 
the  subject  has  been  almost  ignored — overshadowed 
by  the  colossal  controversy  concerning  the  fact  of 
organic  evolution  in  general,  and  the  Darwinian  con- 
tribution to  its  explanation  in  particular.  Latterly, 
however,  the  controversy  ended,  and  ended  con- 
clusively, as  all  controversies  about  verifiable  or 
rational  matters  ultimately  must,  and  biologists 
were  free  to  devote  more  attention  to  the  cardinal 
and  initial  fact  of  variation — upon  which  the  whole 
theory  of  natural  selection  is  based. 

Then  "  a  curious  thing  happened,"  and  it  was  found 

1  See  "  Organic  Evolution  "  in  this  series. 


MENDELTSM  61 

that,  just  at  the  time  when  Darwin's  pen  was  shaking 
the  world,  another  quiet  worker  was  attacking  the 
root  question  in  Austria.  The  pacific  Darwin  had  at 
least  one  champion  who  was  a  master  of  polemics, 
and  his  work  was  soon  noised  abroad.  But  the  Abb6 
Gregor  Mendel  had  no  Huxley ;  and  there  was  noth- 
ing particularly  sensational  about  his  leisurely  but 
scrupulously  honest  and  scientiHc  observations  on 
the  mating  of  different  kinds  of  peas.  Dogmatic 
systems  did  not  worry,  themselves  about  peas,  and 
Mendel  did  not  "  stagger  humanity  "  with  any  asser- 
tions as  to  the  origin  of  our  kind.  Hence  it  was  that 
for  just  thirty  years — and  these,  as  I  have  said,  years 
violently  agitated  about  the  very  questions  which 
Mendel  had  helped  to  solve — scarcely  any  one  had 
heard  of  his  name  or  his  work.  Finally,  Professor 
Hugo  de  Vries,  the  distinguished  botanist  of  Amster- 
dam, rediscovered  it.  He  set  to  work  to  verify  and 
amplify  the  Abbe's  all-but-forgotten  experiments, 
which  had  been  published  in  1865.  In  this  country 
he  gained  an  ally  in  Mr.  Bateson  of  Cambridge,  and 
now  Mendelism  is  perhaps  the  most  bruited  subject 
in  the  whole  realm  of  biology.  It  is  now  beginning 
to  appear  that  the  Abbe's  leisure  hours  served  in 
great  measure  to  elucidate  the  causes  of  variation 
and  the  laws  of  its  occurrence.  He  has  taught  us 
that,  as  we  noted  in  the  first  pages  of  this  book, 
variations  are  not  a  sort  of  "fluke,"  nor  the  results 
of  incompetence  on  the  part  of  the  "  force  "  called 
heredity:  but  that  certain  variations  are  themselves 
the  expression  of  a  form  of  heredity,  ultimately  sub- 
ject to  the  same  laws  and  dependent  on  the  sumo 
sequence  of  events.      It  is  interesting   to  speculate 


62  HEREDITY 

how  long  this  radically  important  work  of  an  Austrian 
abbot  in  the  distant  'sixties  would  have  remained 
in  obscurity  had  not  De  Vries  possessed  the  patience 
and  industry  to  look  into  it,  the  insight  to  recog- 
nise, and  the  ability  to  demonstrate,  its  importance. 

Make  Mendel's  discovery  simple  I  cannot,  the  facts 
being  complex ;  but  I  must  do  my  best.  We  have 
seen  that  each  gamete — of  either  sex — is  formed  by 
a  series  of  divisions  beginning  in  a  germ-mother- 
cell.  Now  the  essence  of  Mendel's  discovery  is  this. 
The  germ-mother-cell,  which  is  about  to  divide  and 
form  the  gametes  that  are  to  reproduce  any  indi- 
vidual in  his  or  her  descendants,  contains  characters 
derived  from  both  the  parents  of  that  individual. 
These  characters  exist  in  the  germ-mother-cell  in 
opposed  pairs — e.g.  a  character  corresponding  to  the 
white  pigmentation  of  the  individual's  father,  and  a 
character  corresponding  to  the  black  pigmentation  of 
the  mother.  When  the  germ-mother-cell  divides  so 
as  to  form  the  gametes,  these  opposed  pairs  of  char- 
acters are  split  up  or  segregated,  the  black  character 
going  to  one  gamete  and  the  white  character  to  an- 
other. Thus  the  gametes,  or  sex-cells,  of  a  grey  in- 
dividual are  not  potentially  grey,  but  either  black  or 
white.  The  germ -mother-cell  was  grey  (so  to  speak) 
like  the  individual,  but  its  greyness  depended  on  the 
possession  of  an  opposed  pair  of  characters,  black  and 
white;  and  these  characters  are  segregated  during 
gametogenesis.  Observe  now  the  result.  The  in- 
dividuals of  the  new  generation  may  be  of  three 
kinds  in  respect  of  the  character  of  colour.  Some 
of  them  will  be  white,  since  they  are  formed  by  the 


MENDELISM  63 

union  of  two  wliitc-bearing  gametes,  some  Vilack,  since 
formed  by  the  union  of  two  black-bearing  gametes, 
and  some  grey  like  their  grey  parents,  since  formed 
by  the  union  of  a  black-bearing  with  a  white-bearing 
gamete.  But  the  gametes  of  this  new  grey  indivi- 
dual will  not  be  grey,  but  black  or  white,  as  before. 

The  discovery  that  variation — e.g.  the  birth  of  a 
black  individual  to  grey  parents — may  really  be  a 
form  of  heredity,  proceeding  according  to  definite 
laws,  and  this  statement  of  the  working  of  the  pro- 
cess, constitute  Mendel's  law  of  seu^recration. 

Such  variations  as  these  may  be  called  mutations, 
in  order  to  distini^uish  their  'Teat  extent.  From 
Mendel's  law  it  follows  that  we  can  no  longer  accept 
the  old  doctrine  quoted  by  Darwin  that  Nature  does 
nothing  by  leaps — ^er  saltuTU.  We  see  that  new 
species  may  suddenly  arise  by  the  operation  of  the 
laws  of  heredity  quite  apart  from  any  slow  accumu- 
lation of  variations  under  the  influence  of  natural 
selection.  As  Bateson  says :  "  The  dread  test  of 
natural  selection  must  be  passed  by  every  aspirant 
to  existence  however  brief":  but  that  expresses  the 
totality  of  its  power.  Natural  selection  selects;  it 
does  not  originate  or  create. 

Space  fails  here  for  the  discussion  of  the  many 
facts  which  "  Mendelism "  and  the  "  mutation 
theory  "  help  to  explain.  What,  for  instance,  could 
be  more  puzzling  than  the  "  limitation  of  licrcdity 
by  sex"  ;  the  transmission  of  hiemophilia  and  colour- 
blindness, for  instance,  from  bleeding  or  colour- 
blind males,  through  normal  females,  to  their  male 
but  not   their   female  descendants  ?  M  or   the  truns- 

^  See  Chapter  XIII.    "  Heredity  ami  Disease." 


64  HEBEDITY 

mission  of  a  "  good  milking  strain  "  by  a  bull,  which 
cannot  produce  one  drop  of  milk  in  a  lifetime  ? 
Yet  these  and  many  other  cases,  not  to  mention  the 
cases  where  heredity  "skips  a  generation,"  can  be 
explained  on  Mendelian  principles.  It  is  only 
necessary  to  postulate  an  intertangling  of  the 
characters  in  the  germ-cells.  Thus,  the  character 
that  will  develop  itself  as  colour-blindness  may  be 
conceived  as  intertangled  with  the  character  that 
makes  for  maleness  of  sex.  They  are  segregated 
together.  In  the  female,  the  character  making  for 
maleness  of  sex  is  temporarily  suppressed,  and  with 
it  the  intertangled  character  of  colour-blindness.  In 
her  male  children  the  two  reappear  together.  The 
characters  that  appear  in  any  individual  are  called 
dominant,  those  that  remain  latent,  to  become 
dominant  in  some  future  individual,  are  called 
recessive. 


CHAPTER    VIII 

KEVERSION 

At  least  three  terms  suggested  themselves  for  the 
title  of  this  chapter — reversion,  regression,  and 
atavism,  each  of  which  hints  at  a  return,  through 
inheritance,  to  a  type  supposed  to  have  occurred  in 
the  ancestry  of  the  individual  under  discussion ; 
or  the  reappearance  in  him  of  latent  ancestral 
characters. 

The  word  atavism  we  may  definitely  abandon — 
especially  since  we  have  more  accurate  terms  to  take 
its  place.     As  Chalmers  Mitchell  points  out,  a  great 


REVERSION  65 

many  supposed  cases  of  atavism  are  merely  cases  of 
normal  variation,  as  ^vhen  a  tall  man  with  short 
parents  is  set  down  as  a  case  of  atavism  because  he 
is  known  to  have  had  a  tall  ancestor.  Other  cases 
of  so-called  atavism  are  better  called  cases  of  rever- 
sion, of  return  to  the  ancestral  type.  Karl  Pearson 
gives  separate  definitions  of  the  terms  atavism 
and  reversion,  but  as  the  terms  are  often  used  inter- 
changeably, or  conversely,  we  may  content  ourselves 
with  speaking  of  reversion  alone.  Thus  when 
Thomson  says,  "  what  are  called  reversions  are  prob- 
ably in  many  cases  misinterpretations,"  he  means 
just  what  Mitchell  means  when  he  says  that  "atavism 
is,  in  fact,  a  misleading  name  covering  a  nuuiber  of 
very  diti'erent  phenomena." 

It  is  scarcely  necessary  to  multiply  in.stances  of 
reversion,  but  I  may  quote  a  typical  one  recorded  by 
Cossar  Ewart.  The  Edinburgh  professor  mated  a 
pure  white  fantail  cock-pigeon  with  a  cross  between 
an  "owl"  and  an  "archangel."  "The  result  was  a 
couple  of  fantail-owl-archangel  crosses,  one  resembling 
the  Shetland  rock-pigeon,  and  the  other  the  blue 
rock  of  India.  Not  only  in  colour,  but  in  shape, 
attitude,  and  movements  there  was  an  almost  com- 
plete reversion  to  the  form  which  is  believed  to  bo 
ancestral  to  all  the  domestic  pigeons." 

The  generally  accepted  explanation  of  reversion 
is  that  it  is  due  to  the  sudden  activity  of  '  latent 
ancestral  units  "  ;  or,  in  the  words  of  Thomson,  "  that 
characters  may  be  latent  for  a  generation  or  for 
generations,  or,  in  other  words,  that  certain  potenti- 
alities or  initiatives  which  form  ])art  of  the  heritage 
may  remain  unexpressed  " — to  tind  expression  at  hist 

£ 


66  HEREDITY 

owing  to  causes  yet  undetermined.  As  Thomson 
says,  "  There  does  not  seem  to  be  anything  in  this 
conception  which  is  at  variance  with  more  securely 
established  generalisations."  The  Mendelians  have 
taught  us  how  characters  may  become  latent  or 
"  recessive,"  subsequently  to  find  expression. 

There  is,  however,  another  way  of  looking  at 
reversion.  It  depends  upon  an  important  conception 
which  must  here  be  briefly  discussed. 

The  "  recapitulation  theory  "  maintains  that  "  onto- 
geny " — the  history  of  the  individual — is  a  recapitu- 
lation, with  abbreviations,  and  gaps,  and  modifications, 
of  "  phylogeny  " — the  history  of  the  race.  This  is  a 
conception  to  which  immense  importance  is  attached 
by  Haeckel  and  Archdall  Reid.  For  some  years  past, 
however,  it  has  been  growing  in  disfavour  amongst 
many  biologists,  who  are  apt  to  declare  that  it  is 
scarcely  more  than  a  misleading  metaphor.  This 
disfavour  is  due,  I  think,  largely  to  a  reaction  from 
the  excessive  dogmatism  and  rigidity  with  which  the 
recapitulation  theory  was  formerly  supported.  But 
even  if  we  admit,  to  the  full,  the  fact  that  the  re- 
capitulation of  its  racial  history  by  the  developing 
individual  is  extremely  blurred  and  often  very  partial 
and  imperfect,  there  yet  remains  sufficient  positive 
evidence  to  show  that  the  theory  is  well  based  on 
facts ;  and  there  can  be  no  question  that  it  is  most 
fruitful  in  its  applications  to  many  and  various  pheno- 
mena of  embryology. 

Now  Archdall  Reid  correlates  the  recapitulation 
theory  with  the  facts  of  reversion.  He  inclines  to 
regard  reversion  not  as  due  to  the  sudden  activity  of 
"latent  ancestral  units,"  but  as  simply  due  to  the 


REVETJSTON  67 

premature  arrest  of  the  process  of  recapitulation. 
The  reverting  individual  is  thus  really  an  example  of 
arrested  development.  It  should  have  showed,  let  us 
say,  the  stages  offish,  amphibian,  mammal,  in  turn; 
but  it  declined  to  undertake  the  complete  recapitu- 
lation of  its  racial  history,  and  thus  appears,  when 
adult,  as  semi-amphibian  instead  of  manunalian. 
In  criticising  supposed  cases  of  reversion,  Thomson 
says,  "  Often  there  is  not  the  slightest  attempt  to 
eliminate  the  phenomena  of  arrested  development." 
Reid  maintains  that  reversion  is  essentially  a  pheno- 
menon of  arrested  development ;  that  is  to  say,  of 
"  incomplete  recapitulation." 

Here,  I  make  no  attempt  to  adjudicate  between 
these  rival  theories,  but  present  them  both,  each 
being  plausible  and  each  of  interest.  I  will  merely 
note  that  Reid,  accepting  the  very  recent  view  that, 
despite  Weismann,  bi-parental  reproduction  is  not  a 
cause  of  progressive  variations,  maintains  it  to  be  a 
cause  of  regressive  variations,  that  is,  of  reversion  to 
type;  the  said  reversion  being  otherwise  expressed 
as  incomplete  recapitulation  of  the  racial  history  by 
the  developing  individual. 

Here  the  biometricians  offer  us  results  of  import- 
ance. Rejecting  Weismann's  theory,  they  maintain 
— as  does  Reid — that  one  of  the  most  important 
results  of  amphimixis  is  the  steady  tendency  to 
maintain — or,  if  necessary,  to  revert  or  regress  to — 
the  type.  "  In  the  tenth  generation  a  man  has  1024 
tenth  grandparents,  and  is  thus  the  product  of  an 
enormous  population,  the  mean  of  which  can  hardly 
differ  from  that  of  the  general  population.  Houco 
this  heavy  weight  of  mediocrity  produces  regression 


68  HEREDITY 

.  .  .  to  type."  This  is  Galton's  law  of  regression 
towards  mediocrity,  already  discussed.  It  follows 
from  it  that  where  there  is  much  in-breeding  the 
weight  of  mediocrity  will  be  less,  and  the  peculiari- 
ties of  the  breed  will  be  accentuated.  The  present 
German  Emperor  might  have  had  4096  ancestors  in 
the  twelfth  generation ;  but,  owing  to  inter-marriages 
{i.e.  in-breeding)  probably  had  only  533.  The  weight 
of  mediocrity  is  less,  the  tendency  to  regression  less, 
and  the  distinctive  characters  of  his  race  thus  more 
likely  to  be  preserved. 


CHAPTER    IX 

THE    THEORIES    OF    HEREDITY 

In  this  very  brief  chapter  we  may  indicate,  side  by 
side,  the  three  theories  of  heredity  which  are  elsewhere 
frequently  alluded  to.  By  theories  of  heredity  we 
mean  explanations  of  the  actual  sequence  of  events 
which  results  in  the  reproduction  of  like  by  like. 
Of  these  there  are  but  three  worthy  of  mention. 

The  oldest  is  Darwin's  theory  of  pangenesis,  Avhich 
supposed  that  every  body-cell  produces  "  gemmules  " 
characteristic  of  it,  which  are  somehow  gathered 
together  in  the  germ-cells.  When  these  develop, 
the  gemmules  reproduce,  in  the  body  of  the  new 
individual,  the  characters  of  those  cells  of  the  parent 
from  which  they  were  derived.  On  this  theory 
nothinsr  could  be  more  natural  than  the  trans- 
mission  of  acquirements.  But  it  is  absolutely  incom- 
patible with  the  facts  known  to  modern  embryology, 


THE    THEORIES    OF    HEREDITY  09 

and  any  one  who  conies  to  consider,  tor  instance,  the 
means  by  which  the  ''gemmules"  are  to  tind  their 
way  to  the  reproductive  glands,  will  agree  that  this 
theory  offers  inherent  ditficulties  of  the  most  formid- 
able character. 

The  second  theory  of  heredity  is  expressed  in  the 
fascinating  conception  of  Weismann — "  the  con- 
tinuity of  the  germ-plasm."  This  has  already  been 
discussed.  Here  we  merely  note  that  it  supplies  a 
most  satisfactory  explanation  of  the  fact  of  heredity ; 
and  that  it  markedly  contrasts  with  the  preceding 
theory  in  its  bearing  upon  the  belief  in  the  transmis- 
sion of  acquirements.  We  may  also  note  some  remark- 
able fashions  in  which  the  theory  may  be  expressed. 
If  it  be  true,  there  is  a  sense,  as  Mr.  Galton  observes, 
in  which  the  child  is  as  old  as  the  parent,  for  when 
the  parent's  body  is  developing  from  the  fertilised 
ovum,  a  residue  of  unaltered  germinal  material  is 
kept  apart  to  form  the  future  reproductive  cells, 
one  of  which  may  become  the  starting-point  of  a 
child.  Further,  the  theory  gives  a  new  meaning  to 
the  saying  that  the  child  is  "  a  chip  of  the  old 
block."  As  Thomson  says,  "  Similar  material  to 
start  with,  similar  conditions  in  which  to  develop, 
therefore,  like  tends  to  beget  like."  Lastly,  note, 
that  on  this  theory  the  daughter  is  really  the  sister 
of  her  mother. 

The  third  and  most  recent  theory  of  heredity  is 
that  of  Oscar  Hertwig.  He  denies  the  existence  of 
a  cardinal  distinction  between  the  germ-plasm  and 
the  plasm  that  goes  to  form  the  individual  body. 
He  observes  that  in  the  higher  plants  there  is  wide- 
spread occurrence  of  tissues  which  have  the  power 


70  HEREDITY 

of  reproduction ;  though  these  tissues  belong  to  the 
individual  body  of  the  plant,  and  are  definitely  dis- 
tinct from  the  special  reproductive  tissues  which  con- 
tain the  "  germ- plasm"  of  Weismann.  Further,  in 
many  of  the  lower  animals  and  plants,  budding  is 
possible  in  almost  any  part  of  the  body.  Further, 
there  are  the  facts  of  regeneration  and  repair,  which 
have  compelled  Weismann  to  introduce  an  extremely 
hypothetical  and  artificial  sub- section  into  his  theory 
of  the  continuity  and  fundamental  distinctness  of 
the  germ-plasm.  But  the  facts  cited  by  Hertwig 
are  intelligible  if  we  assume  that  every  cell  of  the 
body  "  contains  the  germinal  material  for  every  part 
of  the  body,  and  thus,  on  the  call  of  special  con- 
ditions, can  become  a  germ- cell  again."  Hertwig 
supports  his  theory  by  very  numerous  and  varied 
experiments.  These  appear  to  show  that  when 
embryonic  organisms  are  exposed  to  abnormal  con- 
ditions their  cells  can  be  made  to  undergo  unusual 
forms  of  development  and  take  on  functions  other 
than  those  observed  in  other  conditions.  The  in- 
ference is  that  no  particular  cells  are  unalterably 
predestined  for  the  reproductive  or  any  other 
function,  and  that  the  environment  can  cause  this 
or  that  cell,  or  collection  of  cells — according  to 
circumstances — to  devote  itself  to  the  functions  of 
the  '■  germ- plasm." 

It  is  not  here  proposed  to  attempt  the  recon- 
ciliation of  the  diverse  views  of  Weismann  and 
Hertwig.  The  writer's  duty  is  rather  to  note  the 
existence  of  these  differences  of  opinion.  If  the 
theory  of  Weismann  should  appear  to  the  reader 
to  have  received  undue  consideration  in  these  pages. 


THE    THEORIES    OF    IIEREOITY  71 

since  there  are  such  formidable  uhjcctiuns  to  it  as 
Hertwig  has  marshalled,  the  only  defence  to  be 
offered  is  that  Weismann's  theory  does  nevertlieless 
appear  to  be  so  well  founded,  and  so  fruitful  in  the 
deductions  to  be  drawn  from  it,  that  we  may 
legitimately  reduce  our  recognition  of  Hertwig's 
criticisms  to  something  like  the  proportions  of  the 
preceding  paragraphs.  If  the  reader  likes  his 
science  complete  and  exact  he  must  be  content  to 
ignore  biology. 


CHAPTER  X 

THE    INHERITANCE    OF   ACQUIREMENTS 

Doubtless  the  best  method  of  attacking  the  con- 
troversial subject  of  this  chapter  is  to  define  our 
leadmg  terms  with  all  possible  precision. 

For  convenience  in  practice,  or  for  purposes  of 
study,  it  is  possible  to  isolate  from  the  Whole,  which 
we  call  the  Universe,  any  entity  or  aggregate  that 
we  please  and  to  establish  an  antithesis  between 
it  and  all  else.  The  whole  universe,  save  one 
atom,  or  one  electron,  or  one  organism,  is  the  en- 
vironment, the  ''  milieu  environnant "  of  that  atom, 
or  electron,  or  organism.  If  we  are  to  be  philosophic, 
we  must  not  presume  to  say  that  only  certain  entities 
or  aggregates  may  be  thus  conceived.  If  we  may 
select  an  obvious  entity,  so  to  speak,  such  as  a 
dog,  we  may  also  select  a  less  obvious  entity  such 
as  any  organ,  or  any  cell  of  any  organ,  of  that 
dog;  and  may  regard  all  else,  i.e.  the  rest  of  the 
dog  and  all  that  is  not  that  dog,  as    the    environ- 


72  HEREDITY 

inent  of  the  particular  organ  or  cell  under  con- 
sideration. There  can  be  no  philosophic  defence 
of  any  other  course  than  this.  We  must  be  per- 
mitted to  exercise  our  faculty  of  ideal  isolation  on 
any  object  or  any  portion  of  any  object. 

Now,  when  we  come  to  concrete  questions  in 
biology,  we  find  the  importance  of  having  clearly 
understood  the  use  of  the  term  environment.  For 
instance,  in  the  vulgar  use  of  the  term  we  speak  of  a 
dog  (as  an  indivisible  entity)  and  its  environment ; 
and  we  note  that  certain  changes  may  occur  in  the 
dog's  body  as  the  result  of  its  converse  with  the 
environment.  But  in  the  dog's  body  there  are  a 
number  of  germ- cells,  which  Weismann  has  taught 
us  to  consider  as  independent,  as  being  not  really 
part  of  the  dog  at  all,  but  an  immortal  race  of 
which  the  dog  is  the  temporary  trustee.  Thereupon 
it  is  said  that  the  environment  may  affect  the  dog 
but  not  its  germ-cells.  A  corollary  from  the 
doctrine  of  the  "  continuity  "  and  "  immortality " 
of  the  germ-plasm  is  supposed  to  be  the  inviola- 
bility of  the  germ-plasm.  But  when  we  proceed 
to  exercise  the  power  already  demanded  and 
mentally  isolate  the  germ-plasm  of  the  dog,  set- 
ting it  up  in  antithesis  to  all  else,  we  see  that  it 
is  necessary  to  regard  the  body  of  the  dog  as  the 
immediate  environment  of  the  dog's  germ-plasm. 
The  question  then  is  :  In  what  manner,  if  at  all,  is 
the  germ-plasm  of  any  individual  organism  affected 
by  its  immediate  environment — i.e.  by  the  body  of 
the  individual  ? 

For  the  present  we  are  assuming  the  correctness 
of  Weismann's    contention  as   to  the  independence 


THE   INHERITANCE   OF    ACQUIREMENTS       73 

of  the  gerni-pliisiii.  Our  answer  to  the  above  ques- 
tion would  be  very  dili'erent  if  we  were  to  believe  in, 
let  us  say,  Darwin's  theory  of  pangenesis.  Darwin 
suggested  that  every  cell  and  tissue  of  the  body  sent 
a  representative  contribution  to  the  germ-cells,  in 
which  the  individual  was  thus  epitomised.  Hence, 
to  bo  consistent,  if  the  individual  lost  a  limb,  the 
"  gemmules "  that  should  have  been  sent  by  it  to 
the  i^erm-cells  were  wantinir,  and  that  limb  would  be 
wanting  in  the  oftspring.  But  Darwin's  theory  is  not 
held  by  any  one ;  and  we  are  at  present  compelled  to 
consider  the  question  from  the  Weismamiian  stand- 
point. 

Weismann  himself  once  maintained  the  inviola- 
bility of  the  germ-plasm  ;  but  he  has  withdrawn  that 
assertion.  Here  and  there  are  to  be  found  whole- 
hearted Weismannians  who  declare  that  the  germ- 
plasm  is  inviolable,  but  their  position  is,  on  the  face 
of  it,  untenable.  The  germ-plasm  is  a  living  thing, 
and,  like  every  other  living  thing,  has  an  environ- 
ment. It  is  self-evident  that  it  must  have  relations 
with  that  environment.  If  the  immediate  environ- 
ment— the  body  of  the  individual — dies,  so  certainly 
will  the  germ-plasm,  a  fact  which  is  indisputable 
and  conclusive.  What,  then,  are  the  precise  rela- 
tions of  the  germ-plasm  and  its  host  ? 

In  the  first  place,  the  blood  and  lymph  which  are 
produced  in  the  body,  as  a  result  of  its  converse  with 
its  (edible  and  breathabk)  environment,  circulate 
through  the.  germ-plasm.  If  the  body  takes  in 
alcohol,  which  passes  into  the  blood,  the  germ-plasm 
will  necessarily  be  subjected  to  the  inthience  of  that 
druo-.      Further,  if  the  body  be  attacked  by  microbes 


74  HEREDITY 

and  their  soluble  poisons  or  toxins  enter  the  blood- 
stream, they  will  soon  be  brought  into  immediate 
relation  with  the  germ-plasm.  Again,  the  body  con- 
tains many  glands,  such  as  the  thyroid  and  supra- 
renals,  which  produce  ''  internal  secretions  "  that  are 
carried  by  the  blood  to  every  part  of  the  body  and  to 
the  germ-plasm.  Plainly,  any  doctrine  of  the  in- 
violability of  the  germ-plasm  is  utterly  untenable. 
Also — though  this  point  is  more  intricate  and  de- 
bateable — the  reproductive  glands  are  subject  to 
nervous  influences.  Nerves  pass  to  them  from  the 
spinal  cord,  and  no  limit  can  be  set,  in  the  present 
state  of  our  knowledge,  to  the  nature  or  potency  of 
the  nerve-impulses  that  may  thus  connect  the  germ- 
plasm  with  any  part  of  the  body  and,  through  it,  with 
the  remoter  environment. 

If,  then,  we  accept  Weismann's  conception  of  the 
germ-plasm,  we  are  now  in  a  position  tentatively  to 
make  certain  a  priori  assertions  as  to  the  transmis- 
sibility  of  acquired  characters — that  transmissibility 
upon  which  Lamarck  based  his  theory  of  organic 
evolution  and  of  which  AVeismann  denies  the  exist- 
ence. We  must  beware  of  attaching  too  much 
weight  to  a  priori  reasoning,  which  has  led  men 
astray  ever  since  they  began  to  think ;  but  neverthe- 
less we  are  entitled  to  note  the  inferences  which  may 
be  legitimately  drawn  from  our  premisses — whether 
or  no  these  premisses  be  accurate.  Later  we  must 
approach  the  matter  from  the  side  of  observation 
and  a  posteriori  reasoning. 

But  assuming  the  accuracy  of  our  assumptions,  we 
may  say  that  we  can  readily  conceive  of  the  trans- 
missibility of  certain  acquired  characters.      For  in- 


THE    INHERITANCE    OF    ACQUIREMENTS       7.5 

stance,  a  man  acquires  inininnity  to  a  disease.  That 
is  to  say,  his  body-cells,  being  attacked  by  microbes, 
undergo  a  change,  whereby  they  constantly  produce 
an  "anti-toxin"  which  renders  the  further  attacks  of 
these  microbes  futile.  The  production  of  this  anti- 
toxin depends  upon  the  previous  production  by  the 
microbes  of  a  toxin  which  circulates  in  the  blood  and 
lymph,  and  somehow  causes  the  cells  which  it  en- 
counters to  acquire  the  power  of  producing  the  anti- 
toxin. Now  the  toxin,  in  such  a  case,  may  be  carried 
to  the  germ-cells,  and  they,  like  the  body-cells  (which 
were  originally  derived  from  similar  germ-cells)  may 
undergo  the  changes  which  enable  thum  to  produce 
the  anti-toxin  whenever  the  appropriate  stimulus  is 
forthcoming.  Plainly,  in  such  a  case,  we  can  con- 
ceive it  possible  that  the  individual  produced  from 
one  of  these  ^^erm-cells  should  be  immune  to  the 
disease  in  question.  His  father's  acquired  imnumity 
will  thus  have  been  transmitted  to  him. 

Similarly,  other  instances  can  be  quoted  where  the 
modus  operandi  of  the  inheritance  of  an  acquire- 
ment can  be  definitely  conceived.  Now  we  nuist 
remember  that  the  Weismannian  denial  of  the 
transmissibility  of  acquired  characters  was  based 
not  upon  observation,  but  upon  the  doctrine  of  the 
continuity  of  the  germ-plasm.  On  the  Darwinian 
theory  of  pangenesis,  the  -Mo^i-transmissibiHty  of 
acquired  characters  was  inconceivable.  On  the 
theory  of  the  continuity  of  the  germ-plasm,  their 
transmissibility  was  alleged  to  bo  incouceivabio. 
When,  however,  cases  are  cited  wherein  the  trans- 
missibility— whether  it  occurs  or  not — is  conceivable, 
as  in  the  case  quoted,  the  a  pHoin  argument  falls  to 


76  HEREDITY 

tlie  ground ;  and  since  it  no  longer  suffices  to  say- 
that  acquirements  cannot  be  transmitted,  we  must 
resort  to  observation  and  experiment  in  order  to  find 
out  whether  they  are  transmitted. 

But,  on  the  other  hand,  there  remains  a  great 
number  of  acquirements,  the  transmissibility  of 
which  is  indeed  inconceivable  if  we  accept  Weis- 
mann's  theory  of  the  germ-plasm.  Many  of  these 
acquirements  were  once  thought  to  be  transmissible ; 
many  of  them  no  one  ever  thought  transmissible. 
Very  few  students  ever  thought  the  cerebral  change 
which  is  implied  in  the  acquirement  of  knowledge 
to  be  transmissible.  The  manner  in  which  such 
a  change  could  be  reproduced  in  the  germ-plasm 
through  the  agency  of  the  blood,  or  the  internal 
secretions,  or  the  nerves,  is  inconceivable  ;  whilst, 
in  point  of  fact,  we  do  not  find  that  the  child  of  a 
linguist  is  born  with  the  "gift  of  tongues."  But  we 
may  choose  other  instances,  nicely  graduated,  so  that 
it  comes  to  be  a  matter  of  controversy,  and  almost 
of  temperament,  to  say  where  the  possibility  of  trans- 
mission begins  or  ends.  Some  of  these  must  be 
noted ;  but,  meanwhile,  let  me  once  more  insist  that 
we  are  now  dealing  with  the  conclusions  as  to  the 
transmission  of  acquirements  that  may  be  drawn 
from  the  Weismannian  assumption.  We  are  not 
yet  dealing  with  actual  observation  or  experiment. 
Furthermore,  it  must  be  recognised  that  Weismann's 
theory  of  heredity  is  the  most  difficult  to  reconcile 
with  the  transmission  of  acquirements.  If  such  a 
reconciliation  can  here  be  effected,  much  more  easily 
can  the  transmission  of  acquirements  be  reconciled 
with  any  other  theory,  such  as  Hertwig's.^ 

1  See  Chapter  IX. 


THE    INHERITANCE    OF    ACQUIRHMKNTS        77 

Wc  have  already  seen  that  it  is  iiupossiblo  to  re- 
concile Weismaun's  theory  of  the  continuity  of  the 
germ-plasm  with  the  transmissibility  of  such  local 
changes  as  ordinary  injuries  or  mutilations.  Neither 
the  blood-stream  nor  the  existence  of  "  internal  secre- 
tions," nor  the  nervous  connections  of  the  reproduc- 
tive glands,  helps  us  to  conceive  how  a  burn  that 
destroys  the  skin  of  the  father's  back,  let  us  say,  can 
lead  to  the  formation  of  a  scar  on  the  back  of  his 
child.i 

But  the  fact  that  certain  glands  produce  "  internal 
secretions "  which  pass  into  the  blood  and  intluence 
the  rest  of  the  body  has  been  utilised  as  suggesting 
an  hypothesis  which  may  be  of  value.  In  every  case 
where  an  organ  or  tissue  produces  a  "specific  secre- 
tion," that  secretion  may  be  conceived  as  having  a 
specific  action  upon  those  "determinants"  in  the  germ- 
plasm  which  are  destined  to  give  rise  to  the  corre- 
sponding organ  in  a  new  individual.  Dr.  Vernon, 
who  accepts  this  hypothesis,  says :  "  It  is  almost  in- 
conceivable that  each  spot  of  skin  on  the  body,  or 
each  finger,  should  have  a  specific  secretion,  and  that 
an  injury  to  it,  by  changing  its  secretion,  should  so 
aflfect  the  germ -plasm  as  to  produce  a  similar  change 
in  the  corresponding  area  of  skin  of  the  finger  of  the 
offspring";  but  he  is  prepared  to  adduce  the  hypo- 
thesis of  specific  secretions  in  a  large  nundier  of 
cases,  such  as  injury  to,  or  feeble  develo]imont  of, 
the  brain,  active  exercise  of  the  muscles,  and  so 
forth,  where  the  belief  in  the  existence  of  any 
specific  secretion  is  entirely  unsupported  by  any 
recorded   observations.      In  such  cases  it  is  as  yet 

1  It  is  not  asserted  that  this  occurs  1 


78  HEREDITY 

impossible   to  form  any  decision   as    to   the   appli- 
cability of  this  hypothesis. 

Certain  other  transmissions  of  acquirements  are 
compatible  with  Weismann's  theory  of  the  germ- 
plasm,  but  they  may  be  mentioned  only  to  be 
dismissed.  The  first  of  these,  the  influence  of 
"maternal  impressions,"  is  of  interest,  because  it 
serves  to  illustrate  an  important  distinction. 

We  have  already  spent  much  space  in  observing 
the  manner  in  which  we  may  isolate,  for  purposes  of 
thought,  any  entity,  and  then  study  its  relations  to 
all  else.  Now  when  the  male  and  female  nuclei 
have  united  to  form  the  "  segmentation-nucleus  " — 
so  called  since  its  segmentation  will  give  rise  to  a 
new  individual — there  is  plainly  offered  for  considera- 
tion a  distinct  entity — the  embryo.  This  also  has 
its  environment — the  body  of  the  mother.  Nothing 
is  truly  innate  or  inborn  in  the  embryo  save  what 
was  present — as  we  say,  "  in  embryo  " — in  the  seg- 
mentation-nucleus. By  an  absurd  and  childish  con- 
fusion of  thought,  we  persist  in  attaching  quite 
undeserved  importance  to  the  birth  of  any  of  the 
animals  which  are  brought  forth  "  alive."  ^  Hence 
we  speak  of  any  character  present  at  birth  as  con- 
genital— which  is  etymologically  justified;  but  we 
proceed  to  assume  that  congenital  is  synonymous 
with  inherent  or  germinal.  From  our  present  point 
of  view,  it  is  an  irrelevant  detail  that  a  young  mam- 
mal happens  to  leave  its  mother  at  the  ninth  week 
or  month.  During  the  whole  period  that  it  spends 
within  its  mother,  it  is  to  be  regarded  as  an  indi- 
vidual organism,  with  its  own  environment.     If  that 

^  As  if  a  bird's  egg  were  not  alive  I 


THE    INHERITANCE    OF    ACQUIREMENTS        70 

environment    alVects   it    in   any    way  —  stamps   any 
character  upon  it,  we  speak  nonsense  if  we  cl<3clarc 
such  a  character  to  be  a  tiansinitted  ac([uirement. 
Pray  let  us  observe  clearly  this  distinction.     If  the 
mother's  body,  before  conception,  affects,  in  its  role 
of  environment,  the  female  gamete,  in  such  a  fashion 
as  to  stamp  upon  it  a  character  previously  acquired 
by  the   mother,  then   this  gamete,  uniting  with  a 
male  gamete   and  giving  rise  to  a  new  individual, 
may  certainly  transmit  to  it  a  character  acquired  by 
the  mother.     Such  a  character  is  germuial  or  truly 
innate;  for  the  coming  into  existence  of  any  indi- 
vidual— its  birth  as  a  new  individual — coincides  with 
the   conjugation   of  the  gametes  from   which   it  is 
formed.      The   characters   they   confer   upon  it  are 
inherited,  in  the  proper  sense,  and  a  character  ac- 
quired by  the  mother   and  reflected  in  her  germ- 
cells,  would  thus  be  transmitted  to  her  child.     The 
mother's  acquirement  appears  as  a  variation  in  her 
offspring.     This  case  is  fundamentally  distinct  from 
the  impression  of  any  character  upon  the  embryonic 
but,   nevertheless,    distinct  offspring  during  its   de- 
velopment   in    the    body   of   its   mother.      vSuch    a 
character  may  be  present  at  birth,  but  it  is  never- 
theless not  a  variation  but  an  acquirement.     Plainly 
an  acquirement  is  an  acquirement  whether  it  be  ac;- 
quired  five  minutes  or  months  before,  or  five  minutes 
or  months  after,  the  change  of  environment   which 
we  call  birth. 

Hence  it  is  evident  that  the  alleged  results  of 
maternal  impressions — as  when  a  child  is  born  with 
a  withered  limb  resembling  one  the  sight  of  which 
had    powerfully    impressed    the    mother   before    lior 


80  HEREDITY 

child's  birth — would  be,  did  they  occur,  in  no  proper 
sense  instances  of  the  transmission  of  acquirements. 
No  more  would  it  be  a  transmission  of  an  acquire- 
ment for  a  mother  to  pierce  her  child's  ear,  her  own 
having  already  been  pierced. 

Since  we  have  quoted  the  belief  in  the  influence 
of  maternal  impressions,  we  may  briefly  dispose  of  it 
here.  The  alleged  instances  are  easily  explained  in 
any  of  half-a-dozen  different  ways.  Given  a  de- 
formity in  her  child,  no  self-respecting  mother  can 
fail  to  recall  some  accident  of  her  pregnancy  that 
immediately  explains  it.  There  is  no  reason  to  sup- 
pose that  the  few  cases  which  read  most  strikingly 
are  not  explicable  in  accordance  with  the  laws  of 
chance.  No  obstetrician  believes  in  the  power  of 
maternal  impressions,  and  his  knowledge  of  the 
relations  of  the  embryo  to  its  mother  renders  the 
exercise  of  such  power  utterly  inconceivable  to  him. 
Finally,  it  is  to  be  noted  how  ridiculous  is  the  idea 
that  such  transmission  of  maternal  impressions  would 
have  any  bearing  on  the  question  of  this  chapter, 
even  were  it  demonstrated  to  exist.  In  the  asserted 
cases,  the  mother's  acquirement  is  not  a  physical 
deformity,  but  an  impression  of  one ;  the  child, 
however,  does  not  inherit  that  impression,  but  a 
deformity  similar  to  that  which  impressed  the 
mother.  Really  the  whole  theory  is  too  silly  for 
serious  criticism ;  but  it  is  of  interest  as  throwing 
light  upon  the  psychological  processes  of  the  in- 
numerable mothers  who  believe  in  it. 

Here,  most  conveniently,  we  may  also  deal  with 
another  fashion  in  which  it  is  asserted  that  ac- 
quirements may  be  transmitted.     The  influence  of 


THE    INTIKRTTANCR    OF    ACQUIKEMKNTS        HI 

maternal  impressions  and  telegony  may  conveniently 
be  bracketed  together  in  the  reader's  mind  as  entirely 
supposititious  phenomena  which  have  been  quoted  in 
favour  of  the  transmission  of  acquirements.  "  Tele- 
gony is  the  name  given  to  tlic  supposed  fact  that 
offspring  of  a  mother  to  one  sire  may  inherit  charac- 
ters from  a  sire  with  which  the  mother  had  previously 
bred"  (Chalmers  Mitchell).  For  instance,  it  has  been 
said  that  a  mare  which  had  born  a  foal  to  a  (juagga 
subsequently  bore  striped  offspring  to  a  thoroughbred 
horse.  But,  as  Archdall  Reid  points  out,  "  If  the 
white  mother  of  a  half-breed  bear  dark  children  to 
a  white  father,  she  would  not  transmit  anything  she 
acquired,  for  intercourse  with  a  negro  does  not  make 
her  dark."  In  any  case,  it  has  been  conclusively 
proved,  mainly  by  the  work  of  Cossar  Ewart,  that 
telegony  does  not  occur. 

Thus  it  appears  that,  though  the  transmission  of 
certain  acquirements  is  not  incompatible  with  the 
theory  of  the  continuity  of  the  germ-plasm,  yet  the 
scope  of  such  transmission  must  be  relatively  small, 
if  the  theory  be  true.  Darwin's  theory  of  pangenesis, 
as  we  have  seen,  assumes  the  transnn'ssion  of  acquire- 
ments, but  that  theory  is  no  longer  held  by  any  one, 
and  its  repudiation  is  a  blow  to  the  belief  in  the 
transmission  of  acquirements.  Darwin  hiin.solf  be- 
lieved in  such  transmission,  but  the  neo-Darwinians 
or  Weismannians  repudiate  it  almost  without  reser- 
vation, and  with  it  Darwin's  theory  of  pangenesis. 
With  Hertwig's  theory  of  heredity  the  transmission 
of  acquirements  is  quite  compatible. 

Lamarck's  belief  in  the  transmission  of  acquire- 

F 


82  HEREDITY 

ments  was  based  not  on  any  theory  of  heredity,  nor 
upon  any  experimental  evidence.  It  was  merely 
advanced  as  the  most  feasible  explanation  that 
offered  itself  of  the  fact  of  organic  evolution.  Since 
his  day,  however,  the  cases  of  apparent  inheritance 
of  acquirements  have  become  explicable  by  the 
enunciation  of  the  theory  of  natural  selection, 
which  the  neo-Darwinians  regard  as  practically  the 
sole  factor  of  organic  evolution.  Lamarck  supposed, 
for  example,  that  certain  antelopes  run  swiftly 
because  ancestral  antelopes,  in  avoiding  their 
enemies,  developed  the  structures  that  subserve 
speed.  Natural  selection  obviously  furnishes  an 
adequate  explanation  of  the  speed  of  the  antelope 
we  know,  and  so  in  innumerable  cases.  Hence  we 
must  look  for  positive  experimental  evidence  of  the 
inheritance  of  acquirements,  such  as  cannot  be  ex- 
plained by  any  application  of  the  theory  of  natural 
selection.  And  when  we  come  to  inquire,  it  appears 
that  such  evidence  is  very  hard  to  obtain.  The 
effects  neither  of  single  nor  of  long-continued  muti- 
lations (i.e.  mutilations  often  repeated  in  successive 
generations)  are  found  to  be  inherited.  The  inherit- 
ance of  acquirements  due  to  use  or  disuse  is  un- 
proved. The  inheritance  of  the  effects  of  changed 
conditions  of  life  [i.e.  changed  environment)  is 
dubious.  Chalmers  Mitchell  regards  it  as  uncertain ; 
Reid  as  non-existent ;  Vernon  as  proved ;  Weismann 
himself  as  not  proved,  for  he  is  able  to  adduce 
another  explanation  of  the  cases  which  appear  to 
establish  it.  Then,  again,  we  find  no  certainty,  even 
after  years  of  observation,  as  to  the  transmission  of 
traumatic  epilepsy,  i.e.  epilepsy  due  to  the  infliction 


THE    INHERIT ANCE    OF    ACQUIREMENTS        83 

of  gross  injury  l)y  exlerniil  iigencies.  In  short,  I  he 
a  posterioH  evidence  tends,  on  the  whole,  to  negative 
the  theory  that  acquirements  are  transmitted,  but 
cannot  be  regarded  as  conclusive. 

If,  however,  we  consider  certain  facts  of  very  lowly 
organisms,  we  do  seem  to  find  positive  evidence. 
Haeckel,  for  instance,  tirmly  behoves  in  the  inherit- 
ance of  acquirements,  and  cites  certain  known  tacts 
of  bacterial  life.  Disease-producing  bacteria  p;ussed 
through  the  body  of  a  susceptible  animal  are  found 
to  be  increased  in  virulence.  It  is  their  favourable 
environment  that  confers  upon  several  generations  of 
bacteria  their  acquired  exaltation  of  virulence,  and 
they  certainly  transmit  it  to  their  descendants. 
Here,  indeed,  appears  to  be  a  conclusive  instance  of 
the  transmission  of  an  acquirement. 

Thus  we  are  compelled  to  leave  this  controversy 
unsettled.  We  may  tentatively  incline,  however,  to 
the  following  conclusions  : — 

The  transmission  of  certain  accjuirements  is  not 
incompatible  with  Weismann's  theory  of  heredity, 
and  is  perfectly  compatible  with  Her  twig's  theory, 
which  is  far  from  being  disproved. 

Certain  instances  of  transmission  of  acquirements 
appear  to  be  known. 

The  transmission  of  acquirements  is  far  more 
limited,  assuming  it  to  occur  at  all,  than  used  to  bo 
thou'dit. 

However  fully  it  were  admitted,  it  could  not  ex- 
plain all  the  facts  of  organic  evolution. 

Numberless  supposed  instances  of  the  transmission 
of  acquirements  can  be  more  easily  and  satisfactorily 
explained  by  means  of  the  theory  of  natural  selection. 


84  HEREDITY 

The  dogmatists  should  avoid  this  controversy  in 
its  present  stages.  It  will  not  satisfy  their  love  of 
positive  assertions,  and  their  tendency  to  make  such 
assertions  does  not  serve  to  its  solution.^ 


CHAPTER   XI 

THE  RELATIVE  IMPORTANCE  OF  HEREDITY 
AND  ENVIRONMENT 

AccoEDiNG  to  science,  all  living  things  are  deter- 
mined by  two  factors,  heredity  and  environment,  and 
by  those  alone.  This  dogma  applies  to  all  vital  and 
psychic  activities,  the  human  will  most  certainly  in- 
cluded.^ But  ere  we  come  to  look  into  it  more 
closely,  let  us  obviate  a  frequent  misconception. 
Shakespeare's  parents  were  unremarkable,  and  he 
had  six  quite  commonplace  brothers.  Plainly,  then, 
he  did  not  inherit  his  genius ;  and  no  one  will  main- 
tain that  it  was  produced  by  his  environment, — poeta 
nascitur,  non  jit.  What,  then,  becomes  of  the  asser- 
tion that  every  living  thing,  in  all  its  activities,  is 
conditioned  and  determined  by  heredity  and  en- 
vironment ? 

The  objection  depends  upon  a  most  excusable  mis- 
conception. Certainly  Shakespeare's  parents  could 
not  have  written  "  Hamlet,"  even  in  collaboration ; 
certainly  his  environment  did  not  generate  "  Hamlet " 
within  him.     His  genius  was  innate,  inborn ;  the  poet 

1  The  relations  of  psychology  to  this  controversy  are  discussed  in 
the  chapter,  "  The  Origin  of  our  Ideas,"  in  the  author's  companion 
volume  on  "Psychology." 

2  See  "Psychology,"  "The  Human  Will." 


HEREDITY    AND    ENVIRONMENT  85 

is  born,  not  made.  Plainly,  then,  lie  did  inherit  his 
i,^enius ;  not  in  the  sense  that  his  parents  had  it,  but 
in  the  sense  that  it  was  potential  in  those  two  cells 
— or  in  one  of  them,  or  in  their  combination — which 
were  derived  from  his  parents  and  went  to  form  him. 
It  may  be  objected  that  one  cannot  inherit  that  wliicli 
one's  parents  have  not  got ;  but  obviously  our  (piarrel 
is  merely  a  matter  of  terminology.   Let  us  reconsider  it. 

It  is  immediately  evident  that  Shakespeare's  genius, 
like  any  other  character  peculiar  to  him,  such  as  the 
lines  of  his  mouth,  or  the  particular  ratios  of  his 
tinger-lengths,  was  a  variation.  Now,  according  to 
the  old  manner  of  thinking,  this  is  as  much  as  to  say 
that  it  was  not  inherited,  variation  being  the  ''  oppo- 
site" of  heredity.  But  we  have  already  seen  that 
this  view  is  untenable;  that  variation  is  really  a 
form  of  heredity.  Surely  this  must  be  apparent,  if 
we  look  at  the  concrete  case  in  point.  It  may  be 
said  that  Shakespeare  could  not  inherit  what  his 
parents  had  not ;  but  it  cannot  be  gainsaid  tliat,  in 
point  of  fact,  the  particular  variation  whii-h  we  call 
his  genius  was  innate — according  to  the  Latin  tag — 
or,  in  the  language  of  science,  was  germinal.  It  was 
potential  in  the  cell  from  which  Shakespeare  was 
formed;  and  that  cell,  with  its  potentialities,  was 
formed  from  parts  of  two  cells,  one  contributed  by 
his  father,  and  one  by  his  mother.  If,  then,  he  did 
not  get  his  genius  from  his  parents,  it  was  at  any 
rate  potential  in  that  which  he  indisputably  got  from 
his  parents  and  from  which  he  was  formed.  In  this 
sense,  variation  is  a  form  of  heredity. 

Let  us  now  attack  the  familiar  debating-society 
question  as  to  the  relative    impi)rtance  of   heredity 


86  HEREDITY 

and  environment :  understanding  that  the  word 
heredity  is  here  used  in  its  widest  sense,  as  indi- 
cating the  whole  of  that  process  by  which  a  man's 
ancestry  affects  him.  Our  answer  to  the  question  is 
at  once  seen  to  be  clear  and  decisive.  Certainly  the 
poet  is  born  and  not  made ;  but  so  is  the  pig.  The 
pig  is  a  pig  because  it  was  born  a  pig,  not  because 
its  environment  made  it  so.  Similarly  a  man  is  not 
a  horse  though  he  may  have  been  born  in  a  stable. 
Everything  that  constitutes  a  pig  a  pig,  a  man  a  man, 
a  genius  a  genius,  is  really  inborn ;  that  is  to  say,  is 
a  matter  of  heredity  or  ancestry.  Even  if  such  a 
variation  as  genius  seems  to  be  plainly  not  a  matter 
of  heredity  in  the  limited  sense,  it  is  a  matter  of 
ancestry ;  infinitely  more  a  matter  of  ancestry  than 
of  environment.  A  Shakespeare  could  not  be  born 
to  a  sow  or  even  to  a  Fuegian  woman,  no  matter 
what  environment  was  provided.  "Race  is  every- 
thing," said  Disraeli. 

That,  of  course,  is  an  exaggeration ;  and  it  is  there- 
fore necessary  that  we  should  attempt  to  estimate 
the  power  of  environment.  Firstly,  then,  environ- 
ment is  impotent  to  create :  the  poet  is  not  "  made," 
nor  the  pig.  Charm  it  never  so  wisely,  the  environ- 
ment can  only  affect  the  development  of  the  potenti- 
alities already  present.  Every  man  thinks  he  could 
play  billiards  as  well  as  John  Roberts  if  only  he  had 
time  to  practise  enough ;  but  he  is  wrong.  His  in- 
nate characters — and  therefore  his  ancestry — are 
already  determined,  and  infinite  practice  will  not 
make  him  another  Roberts  unless  he  was  born  one. 
Practice  can  make  perfect  only  "  what's  bred  in  the 
bone." 


HEREDITY    AND    KNVITtONMKN'T  87 

Plainly  this  is  a  fact  of  very  great  practical  im- 
portance. Just  as  the  discussion  as  to  the  inherit- 
ance of  acquirements  directly  deals  with  the  utility 
of  education  to  the  future  race,  so  the  fact  that  the 
environment  can  only  determine  ihc  scope  of  innate 
characters  and  can  never  create  even  the  smallest 
character,  affects  profoundly  our  estimate  of  the 
importance  of  education  to  the  hidividual.  What  wo 
commonly  understand  by  education  is  simply  a  parti- 
cular portion  of  the  environment.  In  my  opinion, 
the  only  adequate  and  scientitic  detinition  of  educa- 
tion is  the  provision  of  an  environment.  Thus,  using 
the  word  in  its  largest  sense,  we  see  that  all  experi- 
ence— which  is  converse  ivith  the  environment — is 
educative.  But,  further,  our  study  of  the  relation 
between  environment  and  heredity  prepares  us  to 
appreciate  the  fitness  of  the  word  education.  I  have 
detined  education  as  the  provision  of  an  environment, 
and  we  have  already  seen  that  the  environment  never 
creates  but  merely  acts  on  the  materials  provided  by 
heredity.  Note,  then,  how  tit  the  word  education  is; 
it  signifies  a  leading  forth.  This  is  precisely  what 
the  environment  does;  it  leads  fort  I i  the  characters 
already  present  in  the  individual.  We  must  empha- 
tically realise  that  education — i.e.  the  action  of  en- 
vironment— is  thus  incapable  of  creating  a  poet  or  a 
billiard-player  or  aught  else  ;  but,  if  the  organism  has 
these  potentialities,  education  will  give  them  scope. 

However,  we  uuist  not  omit  the  consideration  of 
the  negative  action  of  the  environment — and  there- 
fore of  education.  The  word  is  not  perfect,  for  it 
ignores  half  the  business  of  education,  which  is 
not  merely  a  leading  forth  but  also  a  forcing  back. 


88  HEREDITY 

Seduced  by  the  current  notion  that  education  is  a 
matter  of  imparting  knowledge,  we  are  apt  completely 
to  forget  this  aspect  of  education,  its  action  in  re- 
pressing certain  potentialities  of  the  germ  so  that 
they  never  realise  themselves.  Yet  it  is  at  least  as 
important  a  function  of  education  to  "  let  the  ape  and 
tiger  die,"  as  it  is  to  educe  the  higher  potentialities. 
This  we  shall  better  understand  if  we  accept  the  pro- 
posed definition  that  education  is  the  provision  of 
an  environment. 

For  observe  that  though  the  environment  can 
never  originate — that  being  left  to  heredity  or 
ancestry  alone — it  can  totally  suppress  any  germinal 
character,  so  that  it  might  never  have  been.  The  in- 
fant Shakespeare,  transported  to  Tierra  del  Fuego, 
had  never  written  a  "  Hamlet."  When  this  considera- 
tion is  well  turned  over  in  the  mind,  we  see  that  the 
action  of  the  environment — i.e.  education — is  not  to 
be  regarded  lightly,  merely  because  we  have  insisted 
upon  the  prime  importance  of  heredity,  and  the  im- 
potence of  the  environment  to  do  more  than  work 
upon  the  material  offered  it.  We  must  remember 
that  the  inherited  potentialities  of  the  germ  are  only 
"potentialities;  no  more.  They  are  entirely  at  the 
mercy  of  environment.  If  that  be  completely  un- 
favourable, the  organism,  with  all  its  innate  char- 
acters, will  die.  If  the  environment  be  favourable 
enough  to  permit  of  life,  it  may  yet  effectively  arrest 
the  expression  of  any  potentiality  given  by  ancestry. 
We  have  already  noted  that  this  power  of  the  en- 
vironment may  be  utilised — for  the  ancestry  includes 
the  "  ape  "  if  not  directly  the  "  tiger  "  of  Tennyson's 
line.     On  the  other  hand,  we  have  to  note  that  this 


HEREDITY    AND    ENVIRONMENT  89 

repressive  action  of  the  environment  may  be  most 
pernicious.  Most  precious  potentialities  j^dven  by 
ancestry  may  as  well  not  have  been  given  at  all, 
so  completely  does  the  environment  ])revent  their 
realisation.  The  illustration  of  the  infant  Shake- 
speare amongst  savages  is  extreme ;  but  every  one 
can  ponder  on  this  point  for  himself.  I  will  merely 
allude  to  the  many  cases  where  some  chance  cir- 
cumstance— i.e.  sonje  fact  of  the  environment — has 
disclosed  powers  of  mind  or  body  which  were  previ- 
ously totally  unknown  to  their  possessor — if  he  can 
be  called  their  possessor  so  long  as  the  environment 
prevented  him  from  entering  into  his  inheritance. 

Observe,  then,  the  admirable  perfection  of  Herbert 
Spencer's  aphorism,  "To  prepare  us  for  complete 
living-  is  the  function  that  education  has  to  discharge." 
The  education,  or  CTivironment,  provided  which  fails 
to  lead  forth  or  which  actively  suppresses  any  de- 
sirable potentiality  of  the  germ  is  inadequate  ;  for 
the  function  of  education  is  to  make  possible  com- 
plete living — that  is  to  say,  the  realisation  of  every 
desirable  potentiality  which  ancestry  has  implanted 
in  the  germ. 

For  instance,  ancestry — by  which  I  mean  the  whole 
past  of  the  race — may  have  implanted  in  the  germ 
a  potentiality  for  the  making  of  music.  Hut  this 
potential  character  inuy  ho  a  varidtion :  the  child's 
father  is  not  musical.  The  father,  unfortunately, 
who  has  not  read  the  story  of  the  little  Handel, 
knows  nothing  about  Spencer's  "complete  living," 
nothing  about  the  duty  of  so  forming  the  environ- 
ment as  to  provide  for  the  education  or  leading  forth 
of  every  desirable  character  of  the  germ,  whether  il 


90  HEREDITY 

be  a  variation  or  not.  And  so  the  boy  has  to  fight 
for  the  education,  or  environment,  which  the  musical 
potentiaHty  in  him  demands  for  its  education.  A 
father  can  never  tell  what  variation  may  bring  forth, 
and  it  is  therefore  his  duty,  since  he  remembers 
that  an  unfavourable  environment  {e.g.  the  wrong 
sort  of  education)  may  suppress  or  atrophy  a  precious 
variation,  closely  to  study  his  child,  so  as  to  discover 
what  its  germinal — innate,  inherited — characters  are. 
Thereupon  he  will  so  construct  the  environment  of 
his  child  (i.e.  will  so  educate  it)  as  to  suppress  the 
bad  potentialities  and  educe  the  good.  Nor  will  he, 
if  he  be  a  student  of  heredity,  too  readily  assume 
that  potentialities  unexpressed  in  himself  may  not 
be  present  in  his  child.  Such  potentialities  may  have 
been  innate  in  the  father  but  suppressed  by  his  en- 
vironment ;  or  their  occurrence  in  the  child  may  be 
a  true  variation,  i.e.  a  character  innate  in  the  child 
but  unpossessed  by  the  parent. 

This  is  one  of  the  cases  where  we  require  to  take 
Dr.  Johnson's  advice  and  "  clear  our  minds  of  cant." 
The  cardinal  primacy  of  heredity  as  compared  with 
environment,  a  primacy  on  which  I  have  surely  insisted 
in  the  preceding  pages,  and  the  marvellous  fashion 
in  which  genius  can  triumph  over  the  environment — 
remould  it  to  its  heart's  desire — and  notably  our  very 
natural  preference  for  the  belief  that  "  genius  will 
out,"  have  led  many  to  maintain  that  Gray  was 
wrong  when  he  wrote  the  familiar  lines  : — 

"  PerhaiDS  in  this  neglected  spot  is  laid 

Some  heart  once  pregnant  with  celestial  fire, 
Hands,  that  the  rod  of  emj^ire  might  have  sway'd, 
Or  wak'd  to  extasy  the  living  lyre. 


HEREDITY    AND    ENVIRONMENT  91 

But  knowledge  to  their  eyes  her  ample  page 
Rich  with  the  spoils  of  time  did  ne'er  enroll  ; 

Chill  penury  repre.ss'd  their  noble  rage, 
And  froze  the  genial  current  of  the  soul." 

We  are  told  that  there  are  no  mute  inglorious  M ikons, 
and  that  in  point  of  fact  genius  always  commands  and 
creates  its  own  environment.  No  fragment  of  proof 
is  ever  offered  in  support  of  these  assertions,  save  the 
argument — which  would  not  impose  upon  a  child — 
that  many  instances  of  the  triumph  of  genius  over 
obstacles  are  recorded  in  biographical  history.  It 
behoves  us  to  understand  that,  though  envir<niment 
cannot  create,  it  has  the  last  word,  and  that  oidy  by 
the  happily  adjusted  interplay  of  heredity  and  en- 
vironment can  any  organism  attain  to  "  complete 
living."  Life  is  the  "  continuous  adjustment  of  inner 
to  outer  relations," 

Hitherto  we  have  discussed  only  the  relative  im- 
portance of  heredity  and  environment  to  the  indi- 
vidual ;  but  what  of  their  relative  importance  to  the 
race  ?  Plainly,  if  acquired  characters  are  not  trans- 
missible, or,  to  state  it  more  comprehensively,  if  the 
action  of  the  environment  upon  the  intlividual  never 
reaches  the  germ-plasm,  then  the  importance  of 
environment  to  the  race  is  nil,  so  far  as  positive 
action  is  concerned,  but  great  in  so  far  as  it  decrees 
which  individual  shall  propagate  his  like  and  whieh 
shall  not.  If,  however,  the  action  of  the  environment 
cannot  be  denied  access  even  to  the  germ-plasm,  then 
its  potencies  are  to  be  regarded  as  immeasurable ;  and 
it  becomes  a  duty  of  mankind  to  exercise  its  power, 
its  unprecedented  power,  of  so  modifying  the  en- 
vironment that  the  germ-plasm  of  any  generation 
may  be  educated  for  the  benefit  of  the  next. 


92  HEREDITY 

CHAPTER    XII 

HEREDITY    AND   "PHYSICAL    DEGENERATION" 

Of  late  we  have  heard  much  of  the  "  state  of  the 
national  physique  "  and  "  physical  degeneration  "  or 
"  degeneracy."  Royal  Commissions  have  been 
hinted  at,  and,  in  the  course  of  time,  some  bright 
statesman  may  even  contemplate  the  advisability  of 
doing  something  to  counteract  a  grave  and  increas- 
ing evil. 

But  it  first  behoves  us  clearly  to  understand  what 
the  evil  really  is.  The  term  "  progressive  degenera- 
tion "  has  been  largely  used  in  the  recent  discussion 
of  this  subject,  and  plainly  contains  a  reference  to 
heredity  as  a  factor  in  the  problem.  Even  wise  and 
serious  students  have  inclined  to  the  popular  view. 
Dr.  William  Hall,  of  Leeds,  for  instance,  who  has 
long  worked  at  the  subject,  was  at  one  time  inclined 
to  believe  that  heredity,  as  shown  in  the  difference 
between  the  Jewish  and  Gentile  children  whom  he 
examined,  might  be  an  important  factor  in  the  pro- 
duction of  this  so-called  "  physical  degeneration." 
But  Dr.  Hall  has  now  entirely  altered  this  opinion, 
and  his  change  of  view  may  be  regarded  as  extremely 
significant.  Dr.  Hall  found  that  the  infinitely 
superior  feeding  and  environment  and  parental  care  in 
general  of  the  Jewish  children  abundantly  accounted 
for  their  great  physical  superiority  to  their  Gentile 
playmates. 

Now  if  it  can  be  demonstrated  that  "  physical  de- 
generation" is  a  misnomer  as  applied  to  the  poor 


HEREDITY  AND  '    PTTYSTCAL  DEOENKRATrnN        \):^ 

children  of  our  cities,  and  that  heredity  is  not  a 
factor  m  the  production  of  their  wretched  physique, 
but  that  their  environment  is  all-important  and  all- 
effective,  the  demonstration  is  to  be  welcomed  and 
recognised  by  those  who  are  striving  to  end  a  state 
of  things  which  is  amongst  the  many  scandals  of  our 
civilisation.  ^ 

It  appears  to  me  that,  both  on  A  priari  and  a 
posteriori  grounds,  we  may  exclude  the  action  ol" 
heredity  in  this  matter. 

The  a  posteriori  grounds  for  ignoring  heredity  are 
as  follows.  In  the  first  place,  none  of  the  actual 
evidence  adduced  is  in  any  way  in  favour  of  the  view 
that  this  is  a  progressive  change — i.e.  a  change  pro- 
gressively increasing  from  one  generation  to  another. 
Dr.  Leslie  Mackenzie,  of  Edinburgh,  is  one  of  the  first 
living  authorities  on  this  matter.  He  says  that  by 
racial  deijfeneration  he  understands  the  transmissit)n 
of  weakness  and  disease  from  one  generation  to 
another,  whereas  the  results  of  his  inquiries  have 
been  to  show  that,  in  the  overwhelming  majority  of 
cases,  there  was  nothing  which  would  have  pre- 
vented the  children  from  growing  up  healthy  and 
fit  had  they  been  reared  in  a  better  environment. 

The  a  priori  argument  against  the  reference  of 
this  "physical  degeneration"  to  the  action  of  heredity 
is  even  more  important.  The  majority  of  those  wlio 
have  asserted  the  occurrence  of  a  progressive  change 
appear  completely  to  ignore  the  fundamental  prin- 
ciples of  the  evolutionary  biology.  They  make  no 
allusion  to  the  fact  that  their  assertions  run  directly 
counter  to  the  law  of  natural  selection.  Those  who 
assert  that  there  is  a  progressive  degeneration  occur- 


94  HEREDITY 

ring  amongst  any  classes  of  our  people  have  it  in- 
cumbent upon  them  to  demonstrate  either  the  falsity 
or  the  suspension  of  the  law  of  natural  selection. 
Biology  asserts  that  hereditary  degeneracy  is  neces- 
sarily doomed  to  extinction,  provided  that  there 
obtain  the  conditions  that  make  for  any  selection 
at  all.  As  long  as  there  is  a  struggle  for  existence 
the  fittest  must  survive.  This  a  ]jriori  argument 
against  the  existence  of  a  progressive  degeneration 
amongst  our  people  is  not  properly  complete  unless 
the  objection  be  met  that  the  "fittest" — as  I  seek 
to  show  in  the  volume  on  organic  evolution — does 
not  necessarily  mean  what  we  call  the  "  best."  The 
fittest  are  merely  the  most  perfectly  adapted  to  the 
conditions  of  the  environment.  No  one,  however, 
will  maintain  that,  even  in  the  highly  "  unnatural " 
environment  of  civilisation,  or  even  the  malignant 
environment  of  crowded  cities,  the  physically  "de- 
generate "  are  any  "  fitter "  than  their  neighbours. 
Indeed,  they  are  obviously  less  so :  they  tend  to  an 
early  death,  to  a  relative  or  absolute  sterility,  and 
their  stock  soon  dies  out. 

Later  we  must  meet  the  argument  of  the  Cessation 
of  Selection,  which  declares  that  heredity  is  a  factor 
in  this  question,  because  the  law  of  natural  selection 
has  been  abrogated  by  civilisation,  and  thus  the 
deteriorates  are  allowed  to  propagate  their  de- 
terioration. 

Meanwhile,  however,  let  us  notice  the  conse- 
quences that  must  follow  upon  the  exclusion  of 
heredity  from  this  problem,  and  the  reference  of  the 
facts  to  the  action  of  the  environment  alone.  This 
advance  in  the  discussion  not  only  greatly  simplifies 


HEREDITY  AND  '  rnVSlCAL  DF=:r;  EN  ERATH  >N   05 

the  subject,  but  it  also  is  exceedingly  comforting. 
Were  we  compelled  to  believe  that  a  representative 
section  of  the  Aryan  race,  such  as  ourselves,  is  under- 
going an  hereditary,  racial  degeneration,  either  owing 
to  some  maleficence  of  the  environment  whioh  made 
the  fittest  of  Spencer's  formula  the  worst  according 
to  our  ordinary  standards,  or  owing  to  the  abrogation 
of  the  law  of  the  survival  of  the  fittest,  or  owintj  to 
a  racial  senility,  then  the  conclusion  would  be  that 
the  white  race  as  a  whole  is  probably  docjmed  to 
extinction — perhaps  hastened  by  th&  incursion  of 
the  Mons^ol.  There  would  thus  be  raised  issues  of 
planetary  significance.  If  however,  the  action  of 
heredity  be  excluded,  we  have  to  face  a  very  much 
smaller  and  very  much  more  hopeful  problem ;  this, 
namely,  that  certain  conditions  of  the  environment, 
such  as  city  life,  bad  feeding,  alcohol,  foul  air,  and  so 
forth,  are  causinsr  a  certain  number  of  individuals  in 
each  generation  to  undergo  a  physical  deterioration 
in  the  course  of  the  individual  lifetime.  Of  these  a 
certain  number  may  possibly  add  hereditary  de- 
generates to  the  next  generation,  but  the  law  of 
natural  selection — if  it  be  still  in  action — ensures 
that  their  race  soon  dies  out. 

Let  us  then  revise  our  terminology.  The  word 
degeneration — a  coming  "  do\vn  from  the  genus" — 
is  certainly  applicable  to  a  progressive  condition  in 
which  each  generation  produces,  in  virtue  of  heredity, 
another  worse  than  itself  This  is  just  the  condition 
which,  as  I  believe,  does  not  hold  in  the  ciuse  under 
discussion.  The  term  deterioixiticm,  on  the  other 
hand,  meaning  simply  "a  beeoming  worse,"  is  more 
fitted  to  the  case  as  1   believe  it  to  be.     A  racial 


96  HEREDITY 

degradation  may  well  be  called  degeneration;  an 
individual  degradation,  due  to  the  malign  influence 
of  the  environment  upon  an  organism  which  is  not 
inherently  or  germinally  degenerate,  is  best  termed 
deterioration.  In  order  to  avoid  the  obvious  im- 
plications of  the  term  degeneration,  its  use  should 
be  abandoned  by  writers  on  this  subject;  unless, 
indeed,  they  believe  that  the  condition  is  an  in- 
herited progressive  degeneration. 

Increasing  this  evil  doubtless  is,  for  the  con- 
ditions of  city  life  are  daily  becoming  the  conditions 
of  more  and  more  of  our  population.  The  denial 
of  the  occurrence  of  a  hereditary  degeneration  by 
no  means  implies  that  the  number  of  persons  physi- 
cally deteriorated  in  this  country  is  not  increasing. 
The  contention  may  be  hazarded  that  the  increase 
in  the  number  of  those  who  thus  deteriorate  is  pro- 
portionate to  the  increase  in  the  urban  as  compared 
with  the  rural  population. 

There  are  falsely  assigned  at  least  three  proofs  of 
physical  degeneration.  These  are — (1)  the  increase 
in  insanity,  which  implies  an  increase  of  morbid 
physical  states ;  (2)  the  steady  fall  in  the  birth-rate ; 
(3)  the  undiminished — though  not  markedly  increas- 
ing— infantile  mortality. 

Of  the  increase  of  insanity  there  is  no  proof,  and 
it  need  not  further  detain  us. 

The  fall  in  the  birth-rate  cannot  possibly  be  re- 
garded as  proof  of  a  progressive  {i.e.  inherited)  racial 
deereneration,  since  its  causes  are  well  known  and 
are  totally  irrelevant.  The  still  scandalous  rate 
of  infantile  mortality  is  alleged  as  a  proof  of  racial 
degeneracy,  it  being  supposed — by  persons  of  extra- 


HEREDITY  AXD  "PHYSICAL  DE(JKNKllATION  "    9? 

ordinary  ignorance — that  the  infants  die  because 
they  are  too  degenerate  to  Hve.  On  the  other  hand, 
we  know  that  a  child  which  has  survived  the  vicissi- 
tudes of  intra-uterine  life,  and  the  dangerous  episode 
of  birth,  has  already  given  proofs  of  vitality,  and  that 
in  ahuost  every  case  there  is  no  inherent  (i.e.  in- 
herited) reason  why  it  should  die.  We  know, 
furthermore,  from  the  comparative  death-rates  of 
breast-fed  and  non-breast-fed  children,  and  from  all 
the  other  relevant  considerations,  that  extraneous 
circumstances  (i.e.  the  conditions  of  the  environ- 
ment) determine  the  overwhelming  majority  of  these 
deaths.  The  infantile  mortality  is  not  a  proof  of 
failing  national  physique,  but  of  the  miserable  in- 
efficiency of  the  national  conscience.  The  infantile 
mortality,  and  the  wretched  physique  of  certain 
classes  of  the  people,  are  both  consequences  of  the 
same  causes,  viz.  the  abominable  environment 
which  we  provide  for  only  too  many  of  the  nation's 
children. 

Let  us  now  consider  three  causes  which,  as  I 
believe,  have  been  falsely  assigned  in  explanation  of 
physical  deterioration,  each  of  these  causes  involving 
an  assertion  in  heredity. 

The  first  of  these  assertions  is  that  the  conlinuous 
increase  of  the  average  age  of  marriage  is  partly 
responsible  for  the  facts.  In  this  country  the 
average  age  of  men  at  marriage  is  now  very  nearly 
28 J  years,  as  compared  with  28  years  a  generation 
ago.  During  the  same  period  the  average  age  of 
women  at  marriage  has  increased  from  about  25 
years  and  8  months  to  26  years  and  ?>  months.  Ihit, 
even  apart   from    the    fact    thai    the   chango    is    so 

o 


98  HEREDITY 

small,  there  is  no  evidence,  or  even  likelihood,  that 
the  gametes  of  a  man  or  woman  of,  say,  thirty-five 
are  in  any  way  inferior  to  those  produced  ten  years 
earlier.  If  increasing  years  did  indeed  affect  the 
germ-plasm,  either  adversely  or  favourably,  or  in  the 
direction  of  greater  or  less  variation,  or,  indeed,  in 
any  fashion  at  all,  the  fact  would  obviously  be  of 
immense  importance  to  the  student  of  heredity. 
But  if  we  confine  ourselves  to  the  normal  reproduc- 
tive period,  there  is  no  reason  to  believe  that  there  is 
any  such  relation  between  the  age  of  the  individual 
and  the  nature  of  the  germ-plasm.  So  far  as  his 
knowledge  of  heredity  can  guide  him,  the  observer 
need  have  no  cause  to  regret  the  present  increase  in 
the  average  age  at  marriage — an  increase  which  may 
otherwise  be  welcomed  for  many  reasons.  But  it  is 
well  to  recognise  that  there  may  be  facts  of  import- 
ance with  which  we  are  yet  unacquainted  as  to  the 
influence  of  the  age  of  the  individual  upon  the  germ- 
plasm.  So  far  we  are  able  to  make  any  definite 
assertion  only  as  to  the  relation  between  size  of 
family  (which  is  obviously  correlated  with  the  age  of 
the  parents)  and  mental  characters.  Thus  Havelock 
Ellis  ^  finds  that  genius  is  one  of  the  abnormalities 
associated  with  families  of  large  size.  This  holds 
good  whatever  century  be  taken  for  study.  Galton 
("  English  Men  of  Science ")  obtained  a  like  result, 
as  have  other  students.  Toulouse,  Magri,  Langdon 
Down  and  Cassel  are  quoted  by  Havelock  Ellis  as 
having  shown  that  insanity,  imbecility,  hysteria,  and 
neurasthenia  are  more  frequent  in  large  than  small 
families.    It  would  obviously  be  premature  to  attempt 

1  "  A  Study  of  British  Genius,"  1904,  pp.  106  et  seq. 


HEREDITY  AND  "PHYSICAL  DECJENER ATIOX        00 

any  interpretation  of  these  facts.  It  sutHces  that  the 
avaihiblc  evidence  by  no  means  supports  the  view 
that  the  present  state  of  the  lower  cLasses  of  our  urban 
populations  may  bo  ascribed,  even  in  part,  to  the  in- 
crease in  the  average  age  of  the  parents  of  this  people. 

The  second  cause  assigned  without  proof  as  ex- 
planatory of  the  imperfect  physi(pie  of  many  is  the 
alleged  "  multiplication  of  the  unfit " — the  produc- 
tion of  degenerates  by  degenerates.  To  this  allusion 
has  already  been  made.  It  assumes,  first,  the  ability 
of  the  degenerate  to  propagate.  Now  it  is  hn possible 
to  maintain  that  no  degenerate — we  assume  that  this 
word  answers  to  a  fact  and  not  a  fiction — is  capable 
of  reproduction;  but  it  is  worth  rememl)ering  that 
a  relative  or  absolute  sterility  is  a  distinguishing 
mark  of  degeneracy.  The  assertion  of  the  "  multipli- 
cation of  the  unfit"  assumes,  secondly,  the  cessation 
of  selection,  or  its  partial  supersession  by  the  social 
conditions  of  our  time.  This  matter  will  shortly  be 
dealt  with. 

The  third  falsely  assigned  explanation  of  the  un- 
satisfactory state  of  the  national  physique  is  that 
based  upon  the  assumption  of  a  general,  inherent, 
inevitable,  national-racial  decadence — the  multiplica- 
tion of  adjectives  being  in  inverse  proportion  to  that 
of  evidence  in  support  of  this  contention.  It  is 
asserted  that  the  Anixlo-Saxon  race  has  reached  its 
zenith    and    is   now   in    process   of    decline.^      The 

1  It  has  already  been  noted  that  Dr.  Hall,  of  Leeds,  was  fonnfrly 
inclined  to  postulate  some  racial  law  of  rise  and  fall  in  exi'laua- 
tion  of  the  differences  which  he  observe*!  between  Jew  and  Gnitile 
children  in  tliat  city.  But  now  lie  attributes  lliese  difTen-ncea 
to  the  fact  that  "the  Jews  know  Low  to  fee«l  their  children 
properly." 


1 00  HEREDITY 

physical  deterioration  witnessed  in  our  great  towns 
and  cities  is  cited  as  a  ^posteriori  proof  of"  this  racial 
senility,  and,  though  no  explanation  of  the  details  of 
the  process  is  advanced,  a  priori  arguments  are  also 
forthcoming.  In  the  first  place,  there  is  the  argu- 
ment from  analogy.  As  the  individual  grows  and 
reaches  maturity,  and  declines  and  dies,  so  plainly 
must  the  race.  This  type  of  argument  appeals  to 
many  minds,  but  it  is  worse  than  worthless.  It 
needs  no  expert  logician  to  detect  the  palpable  fallacy 
involved.  Because  the  race  may  be  likened  to  a 
living  entity,  such  as  the  individual,  whatever  is  true 
of  the  individual  is  true  of  the  race !  On  the  con- 
trary, the  individual  and  the  race  are  far  more  truly 
antithetic  than  analogous.  The  profound  contrast 
between  them  is  that  the  individual  is  mortal,  the 
race  immortal.  Being  mortal,  the  individual  must 
die — that  is  evident ;  being  immortal,  the  race  does 
not  die.     Hence  the  suggested  analogy  is  worthless. 

Another  argument  is  based  upon  what  is  commonly 
called  history.  Other  races  have  risen  and  fallen, 
and  so  must  this.  Here,  again,  is  one  of  the  many 
accepted  beliefs  which  are  accejDted  simply  because 
they  are  not  analysed.  No  known  factor  or  fact  of 
organic  evolution  or  heredity  helps  us  in  the  smallest 
degree  to  understand  how  or  why  such  an  inevitable 
decadence  should  occur.  It  is  quite  incomprehensible 
that  the  physical  factors  of  the  germ  that  make  for 
success  should  contain  within  themselves  a  principle 
of  decay.  When  we  come  to  look  at  the  facts  of 
history  more  closely,  we  discover  abundant  evidence 
to  show  that  the  phenomena  of  the  rise  and  fall  of 
nations  are  not  dependent  upon  physical  or  organic 


HEREDITY  AND  "PHYSICAL  DEGENERATION"   101 

factors,  but  upon  psychical,  sociol()<,ncal,  super-orf^unic 
factors.  The  decliue  of  nations  is  not  a  theme  tor 
the  biologist,  the  student  of  heredity,  hut  f(jr  the 
sociologist  and  the  moralist.  iUit  it  is  highly 
necessary  for  the  student  of  heredity  to  atlirm,  and 
again  and  again  to  affirm,  that  Ice  knows  no  cause 
whatever  why  nations  should  decay.  His  study 
throws  no  light  on  the  phenomenon,  or,  rather,  it 
does  throw  a  light  upon  it  by  demonstrating  that 
there  are  no  facts  or  factors  of  heredity  that  exphiin 
it.  Hence  when  the  moralist  seeks  to  exphun  the 
causes  of  national  decay  he  is  justitied  in  his  preach- 
ing by  the  positive  assertion  of  the  biologist  that 
there  are  no  physical  facts  which  explain  such  de- 
cadence, and  should  the  historian  seek  to  save 
himself  the  trouble  of  finding  the  true  explanation, 
and  hint  that  the  decay  of  nations  is  due  to  some 
obscure  laws  of  heredity  as  yet  unclucidated,  his 
listeners  must  be  warned  that  the  student  of 
heredity  will  countenance  no  such  explanation.  In 
the  organic  world  success  makes  for  more  success ; 
it  is  not  to  the  facts  of  the  germ-phism,  but  to  the 
facts  of  mind  and  morals,  that  we  must  attribute 
the  decline  and  fall  of  any  empire  or  nation.  Thus 
a  nation  may  be  tottering  to  its  fall,  whilst  its 
stalwart  sons — "  superb  specimens  of  physical  man- 
hood"— are  breaking  all  athletic  records. 

One  important  point  remains  to  bo  considered — 
the  alleged  cessation  of  selection.  If  selection  has 
ceased,  then  the  a  priori  objection  to  the  belief 
in  a  progressive  physical  degeneration  is  disp(.).sed 
of.      If    there    is   no    selection,   plainly,     the     unLit 


102  HEREDITY 

are  free  to  multiply,  if  their  unfitness  does  not 
interfere  with  their  reproductive  powers;  and  the 
further  question  will  then  be  raised  as  to  how  far 
their  unfitness,  whether  acquired  or  germinal,  is 
transmissible. 

But  if  the  biometricians  have  conclusively  proved 
anything,  it  is  that  selection  has  not  ceased  among 
civilised  peoples.  As  Professor  Pearson  has  said, 
no  one  can  look  at  a  mortality-table  and  believe 
that  selection  no  longer  occurs ;  and  as  Reid  says : 
"  If  natural  selection  no  longer  eliminates  the  unfit 
among  civilised  peoples,  it  is  evident  that  most  people 
must  die  of  old  age,  or  else  that  the  elimination 
is  not  selective.  But,  as  a  fact,  millions  of  people 
perish,  even  in  England,  which  is  highly  civilised, 
before  or  during  the  child-bearing  age,  nearly  all 
of  whom  are  eliminated  because  they  are  consti- 
tutionally incapable  of  surviving  under  the  ordinary 
conditions  of  the  environment  in  which  they  find 
themselves." 

The  vast  majority  of  human  deaths,  especially 
among  civilised  peoples,  are  due  to  disease ;  and 
disease  is  unquestionably  selective.  Thus,  though 
we  may  freely  admit  that  the  general  tendency  of 
many  charities,  of  many  laws,  and  the  work  of  the 
medical  profession  is  directed  against  the  operation 
of  natural  selection,  yet  this  factor  of  evolution  is 
very  far  from  having  ceased,  even  amongst  the  most 
civilised  peoples.  It  cannot  be  argued  that  the 
physical  deterioration  witnessed  in  our  cities  is  the 
result  of  the  cessation  of  natural  selection. 

On  the  other  hand,  we  must  not  flatter  ourselves 
that  no  action  on  our  part  is  required  ;    that  the 


IIEUEDITY  AND  "I'lIYSICAL  DI!:GENKKATI()N"   lO.'J 

selective  process  is  duini,^  all  that  any  soluclivc 
process  can  do.  On  the  contrary,  we  must  recognise 
that  certain  modern  doctrines  and  practices  do  tend  ^ 
towards  the  most  unwise  and  disastrous  limitation 
of  the  action  of  natural  selection.  It  is  not  well 
that  civilisation  should  interfere  with  natural  selec- 
tion, and  artificially  facilitate  the  reproduction  of 
those  attticted  with  certain  forms  of  vice  or  mental 
or  physical  disease.  Furthermore,  it  is  our  duty, 
having  recognised  the  potency  of  heredity,  and 
therefore  the  importance  of  the  principle  of  selection, 
to  aid  its  action,  and  extend  it  in  accordance  with 
our  ideals.-  If  artificial  selection  is  worth  while 
in  the  case  of  race-horses,  it  is  worth  while  in  the 
case  of  man. 


CHAPTER   Xlli 

HEREDITY    AND    DISEASE 

The  title  of  this  chapter  covers  several  subjects 
which  are  not  closely  related  to  one  another,  hut 
which  may  be  conveniently  dealt  with  under  this 
heading.  The  first  of  these  is  of  little  importance 
in  connection  with  the  theory  of  heredity,  but  others 
are  of  high  theoretical  interest. 

The  inheritance  of  disease  is  a  subject  on  whieh 
our  opinions  have  lately  undergone  a  profound 
revolution.  This  is  indeed  to  be  expected,  if  wo 
remember  that    it   is  but   a    few   decades   since    wo 

1  See  the  chapter,  "  Socialism,"  in  the  volume  •'  Sociolofry." 
«  See  the  chapter,  "  The  Future  Evolution  of  Man,"  in  the  volume 
"  Organic  Evolution." 


104  HEREDITY 

gained  any  considerable  knowledge  of  the  causation 
and  essential  nature  of  the  vast  majority  of  all 
diseased  conditions.  The  study  of  the  inheritance 
of  disease  entered  on  its  first  fruitful  stasfe  when 
Pasteur  and  his  followers  taught  us  that  nearly 
all  disease  is  due  to  the  invasion  of  the  body  by 
microbes  or  bacteria.  As  it  is  daily  becoming  more 
difficult  to  name  any  important  diseases — save  prob- 
ably cancer — that  are  not  of  microbic  origin,  we  shall 
here  take  for  granted  a  practical  identity  between 
"  disease  "  and  "  disease  of  bacterial  causation." 

Plainly  the  greater  part  of  our  discussion  will  have 
little  bearing  at  this  stage  on  the  general  problems 
of  heredity,  but  will  be  concerned  rather  with  the 
habits  of  various  bacteria,  and  the  possibility  of 
their  communication  to  the  germ  or  the  embryo. 
Let  us  take,  for  instance,  the  most  important  of  all 
diseases,  which  probably  slays  about  one  in  five,  six, 
or  seven  of  all  the  human  beings  that  die  upon  the 
earth.  We  now  know  that  "consumption"  and  a 
hundred  other  diseased  conditions  are  due  to  the 
invasion  of  some  part  of  the  body  by  a  minute  plant 
called  the  tubercle  bacillus  or  hacillws  tuberculosis. 
It  is  still  widely  believed  that  tuberculosis  is 
hereditary. 

But  to  the  modern  pathologist  this  statement  can 
only  mean  that  the  tubercle  bacillus  may  invade  the 
germ-cells  by  direct  passage  from  an  infected  parent ; 
or  may  enter  the  embryo  from  the  body  of  an 
infected  mother.  Thus  the  child  at  birth  will  contain 
tubercle  bacilli.  This  the  pathologist  would  term 
congenital  or  hereditary  tuberculosis.  Plainly,  how- 
ever,  it   would    be    desirable    to    use    these    terms 


HEREDITY    AND    DISEASE  1  O.J 

more  accurately.  The  entrance  of  bacilli  from  the 
body  of  the  mother  into  the  body  of  an  unborn 
child  is  not  to  be  distinguished  from  the  point  of 
view  of  the  student  of  heredity,  from  the  infection 
of  the  child,  after  birth,  by  bacilli  derived  from  the 
mother;  nor  is  this  to  be  distinguished  from  the 
spread  of  infection  from  the  mother  to  any  other 
child  or  adult.  It  is,  doubtless,  of  great  pathological 
and  practical  interest  and  importance  to  discuss 
the  possibilities  of  the  infection  of  the  embryo,  or 
foetus,  by  the  mother,  but  the  presence  of  tubercle 
bacilli  in  the  child  at  birth,  as  a  result  of  such  in- 
fection, should  properly  be  called  conigp/nital  not 
hereditary  tuberculosis.  One  organism  living  within 
another  which  is  the  host  of  a  parasite,  such  as  the 
tubercle  bacillus,  may  well  be  specially  liable  to  infec- 
tion ;  but  that  fact  is  of  little  interest  to  the  student  of 
heredity,  which  is  the  tendency  of  like  to  beget  like. 

The  point  must  be  insisted  ujxai,  for  current 
medical  and  popular  nomenclature  takes  no  cog- 
nisance of  what  is  really  a  cardinal  distinction.  The 
ante-natal  infection  of  an  embryo,  or  foetus,  is  a 
special  problem  in  the  general  subject  of  infection. 
Strictly  speaking,  it  has  nothing  whatever  to  do  with 
the  subject  of  heredity.  Another  instance,  by  no 
means  uncommon,  is  worthy  of  citation.  Tin- 
disease  known  as  acute  rheumatism,  or  rheumatic 
fever,  is  due  to  a  particidar  microbe  called  the 
diplococcus  rheumaticvs.  This  microbe  not  infre- 
quently attacks  a  pregnant  woman.  During  the 
course  of  her  attack  of  rheumatic  fever,  the  poisons 
produced  by  the  diplococcus  circulate  through  her 
blood,  and  only  too  often  attack  the  valves  of  her 


106  HEREDITY 

heart,  especially  those  of  the  left  side  of  the  heart, 
which  is  subjected  to  greater  strain.  But  these 
poisons,  or  toxins  (the  plural  is  used  not  because 
there  is  definite  evidence  that  there  are  more  than 
one,  but  because  we  know  little  of  their  nature  as 
yet,  the  diplococcus  having  only  very  recently  been 
discovered),  are  also  contained  in  the  blood  which 
the  mother  sends  to  the  placenta ;  and  that  organ  is 
apparently  unable  to  prevent  their  passage  from  the 
maternal  to  the  foetal  circulation.  Hence  the  toxins 
may  attack  the  heart  of  the  child,  especially  the 
valves  of  the  right  side,  which  are  subjected  to  the 
greater  strain  in  intra-uterine  life.  The  child  is  thus 
born  with  "  congenital  heart-disease,"  or,  to  use  the 
doctor's  slang,  "  a  congenital  heart."  Now,  observe  the 
broad  results  as  they  would  appear,  say,  thirty  years 
ago,  when  the  bacterial  origin  of  rheumatic  fever 
was  not  even  suspected.  The  mother  has  the  rheu- 
matic "  diathesis,"  or  "constitution,"  or  "dyscrasia" 
— the  Qfreater  the  iOTorance  the  more  luxuriant  the 
terminology — which  results  in  heart-disease.  The 
child  is  born  with  heart-disease  absolutely  identical 
save  for  a  slight  difference  in  its  site.  Plainly  the 
child  has  inherited  the  maternal  "  diathesis." 

But  now  we  know  the  actual  facts  of  the  case,  and 
we  perceive  that  they  really  have  nothing  to  do  with 
the  problems  of  heredity  proper.  The  baby's  heart- 
disease  is  not  due  to  its  having  inherited  the  "  rheu- 
matic diathesis  "  from  its  mother,  but  to  the  circum- 
stance that  during  its  life  within  the  mother  certain 
poisons  circulating  in  the  mother's  blood  happened 
to  pass  into  its  blood  and,  as  is  quite  intelligible, 
caused  injuries  within  its  body  similar  to  those  pro- 


nERI<]DITY    AND    DISEASE  107 

(luced  within  the  body  of  the  mother.  Profoundly 
interesting  and  important  all  this  doubtless  is  ;  and  so 
are  a  hundred  other  cases  more  or  less  parallel  with 
it,  such  as  the  killing  of  the  child  by  the  giving  of 
poison  to  its  mother,  or  the  possible  treatment  of  the 
suckling  child,  after  birth,  by  giving  castor  oil  to  its 
mother.  But  these  are  not  cases  of  heredity,  save  in 
so  far  as  the  child's  tissues  inherit  those  characters  of 
the  maternal  tissues  which  make  them  respond  in  cer- 
tain fashion  to  the  action  of  the  rheumatic  toxin,  or 
mercury,  or  castor-oil.  This  we  now  see  clearly,  but  it 
is  well  to  remember  the  totally  dillerent  aspect  which 
the  facts  necessarily  wore  when  the  nature  of  rheu- 
matic fever  was  unknown.  Meanwhile  there  remain 
not  a  few^  diseases,  such  as  gout,  of  which  the  causation 
is  still  unexplained  and  about  the  inheritance  of  which 
it  will  be  well  to  preserve  some  reticence  until  haply 
we  may  "  know  what  we  are  talking  about." 

But  before  we  leave  this  part  of  our  subject  we  may 
note  one  or  two  very  interesting  facts  which,  as  we 
are  now  able  to  recognise,  are  not  facts  of  heredity, 
though  they  may  appear  to  be  such  at  first  sight. 
We  have  already  observed  how  the  passage  of  poisons 
from  the  blood  of  a  mother  to  the  blood  of  the 
unborn  child  may  give  rise  to  the  appearance  of 
inherited  disease.  Similarly  a  child  may  acquire 
immunity  from  various  diseases  or  poisons,  but  this 
immunity  is  acquired — not  inherited,  or  innate,  or 
"natural."  For  instance,  Ehrlich,  the  greatest  living 
authority  on  immunity,  has  shown  that  the  oflspring 
of  mice  who  had  acquired  an  imnuinity  to  the  action 
of  certain  poisons,  were  themselves  immune,  if  both 
parents  or  the  mother  alone  had  been  immunised  ; 


108  HEREDITY 

but  were  susceptible  if  the  father  alone  had  been 
immunised.  He  further  proved  that  this  so-called 
inheritance  of  immunity  is  not  a  true  inheritance — 
were  it  so,  it  would  clearly  be  a  case  of  the  trans- 
mission of  an  acquired  character — but  is  an  acquire- 
ment of  the  young  mouse,  partly  due  to  the  passage 
before  birth,  of  certain  substances  into  its  blood  from 
the  blood  of  the  mother  and  partly  due  to  a  subse- 
quent transference  of  these  substances  by  means 
of  suckling.  Plainly  it  is  all  one  to  the  student 
of  heredity  whether  the  young  mouse  acquired  its 
immunity  from  the  blood  with  which  the  mother  fed 
it  before  birth  or  from  the  milk  with  which  she  fed 
it  after  birth.  The  case  is  not  one  of  heredity. 
Similarly  the  human  infant  may  acquire  immunity 
through  its  mother's  milk.  Ehrlich  is  inclined  to 
think  that  the  very  general  immunity  of  the  human 
infant  from  a  number  of  infectious  diseases,  such  as 
mumps,  scarlet  fever,  and  measles,  during  the  first 
year  of  life,  is  due  to  its  constant  imbibition  in  its 
mother's  milk  of  protective  substances  poured  into 
the  mother's  blood  by  her  body-cells  in  consequence 
of  their  acquired  immunity  to  the  diseases  in  ques- 
tion. Plainly  this  also  is  no  case  of  heredity  ;  for  the 
sequence  of  events  could  be  paralleled  by  the  pre- 
cipitation of  these  protective  substances  from  the 
milk  of  any  immunised  animal,  and  their  adminis- 
tration to  the  child.  Problems  of  heredity  will  arise 
when  we  ask  ourselves  whether  the  immunity 
acquired  by  a  mother  or  a  father  can  so  aifect  the 
germ-plasm  as  to  endow  the  offspring  with  a  truly 
inherited  immunity.  We  have  already  seen  that  in  the 
case  of  the  paternal  mouse,  immunised  against  certain 


HEREDITY    AND    DISEASE  100 

poisons,  the  gerin-cclls  were  unable  to  transmit  sucli 
ininninity.  Apparently  they  were  unatVected,  even 
by  the  presence  of  these  poisons  in  the  blood  that 
passed  through  the  reproductive  glands. 

Let  us  now  revert  to  the  typical  question  of  the 
inheritance  of  tuberculosis,  and  inquire  as  to  th(3 
occurrence  of  anything  that  may  properly  bo  termed 
a  fact  of  heredity. 

It  is  conceivable,  as  we  have  already  observed, 
that  the  male  or  female  gametes  of  any  tuberculous 
parent  might  be  infected  with  tubercle  bacilli,  and 
the  changes  they  wrought  in  such  gametes  w(ndd 
doubtless  affect  the  "  segmentation  nucleus "  (the 
nucleus  of  the  first  cell  of  the  new  organism);  but 
even  this  state  of  affairs  is  scarcely  cognate  to  the 
problem  of  heredity  proper,  though  it  nuist  later 
be  considered. 

In  point  of  fact,  however,  so-called  hereditary  or 
congenital  tuberculosis  is  practically  non-existent; 
one  or  two  cases  have  been  recorded,  but  they  are 
merely  pathological  cariosities.  The  germ-cells  of 
tuberculous  parents  are  not — save  perhaps  once  in 
millions  of  cases — infected  by  the  tubercle  bacillus. 
Furthermore,  it  has  been  discovered  that  the  pla- 
centa, or  after-birth,  the  organ  of  communication 
between  the  mammalian  mother  and  her  unl)orn 
child,  possesses  the  power  of  filtering  the  blood  ^ 
which  passes  through  it,  so  that  bacteria  whicli 
may  be  present  in  the  maternal  blood  do  not,  save 
in  a  quite  infinitesimal  proportion  of  cases,  gain  en- 
trance to  the  body  of  the  child.     Thus  it  may  be 

^  This  is  loosely  expressed,  but  with  sunicicnl   jiccurarv  for  fho 
present  purpose. 


110  HEREDITY 

fairly  stated — the  exceptions  being  negligible — that 
the  new-born  baby  is  "aseptic,"  "sterile,"  or  "germ- 
free,"  even  though  one  or  both  of  its  parents  may 
be  subjects  of  microbic  disease.  This  assertion  is 
tantamount  to  a  denial  that  the  inheritance  of  disease 
is  a  fact  of  any  importance  or  frequency. 

But  now  we  must  proceed  to  make  a  most  im- 
portant qualification  of  this  very  important  state- 
ment— a  qualification  which  enables  us  to  answer 
the  very  just  criticism  that,  despite  our  theories, 
germ-diseases  are  daily  seen  with  most  suggestive 
frequency  in  parents  and  their  children.  It  is  true 
that  this  criticism  is  largely  irrelevant ;  for  the  ex- 
planation of  the  occurrence  of  the  same  disease  in 
parents  and  children  often  is  that  the  children  have 
become  infected  by  their  parents.  A  recent  writer 
even  inclines  to  the  view  that  the  apparent  inherit- 
ance of  some  factor — immediately  to  be  considered 
— in  tuberculosis  is  largely  to  be  accounted  for  by 
the  fact  that  the  children  of  tuberculous  parents 
are  so  gravely  exposed  to  infection.  Nevertheless, 
there  doubtless  is  a  factor  in  tuberculosis,  and  the 
many  diseases  of  which  we  have  taken  it  as  the  type, 
which  is  inherited — the  factor  of  susceptibility. 

In  all  microbic  diseases  there  are  two  cardinal 
factors :  the  presence  of  the  causative  parasite,  and 
the  receptivity  of  the  host.  Or,  if  we  figure  the 
disease  as  a  crop  or  harvest,  we  may  say  that  it 
depends  upon  the  mutual  fitness  of  the  seed  and  the 
soil.  This  becomes  apparent  directly  we  accept  the 
germ  theory  of  disease.  A  cat  may  suffer  from  diph- 
theria, and  so  may  a  baby:  either  may  infect  the 
other.     But  no  cat  ever  caught  scarlet  fever  from 


HEREDITY    AND    DISEASE  1  1  1 

a  baby.  Similarly  the  microbes  of  certain  diseases 
demand  for  their  soil  the  tissues  of  man  or  of  a  hi^rher 
ape,  the  lower  ape,  the  lemur,  and  all  other  animals 
being  insusceptible  or  immune.  Again,  there  is  one 
kind  of  sheep  Avhich  is  immune  to  a  disease  that 
readily  attacks  all  other  sheep ;  and  so  on.  without 
limit.     Plainly  there  is  a  question  of  heredity  here. 

When  we  attempt  to  name  the  factors  of  suscepti- 
bility or  of  imnumity  we  find  ourselves  in  ditliculties. 
For  immunity  or  heightened  susceptibility  may  be 
acquired  by  the  individual  as  a  result  of  actual 
experience  of  the  disease.  Immunity  or  suscepti- 
bility may  vary  in  its  degree  from  day  to  day,  or 
from  decade  to  decade.  It  may  be  relative  or 
absolute,  temporary  or  permanent,  natural  or  ac- 
quired. But  in  every  case  true  immunity  or  sus- 
ceptibility must  ultimately  depend  upon  the  facts 
of  cell-chemistry,  and  in  many  cases  these  facts 
must  be  of  very  ancient  origin.  The  natural  sus- 
ceptibility of  the  chimpanzee  and  of  man  to  a 
certain  disease  plainly  depends  upon  inborn  charac- 
ters which  have  been  transmitted  through  thousands 
of  generations.  Their  immunity  to  the  tsetse-fly 
disease  of  the  horse  is  similarly  a  fact  of  heredity. 

But  we  have  already  seen  that  imnumity  or 
susceptibility  may  be  confined  to  certain  varieties 
within  a  species,  as  in  the  case  of  the  sheep.  Simi- 
larly it  appears  that  different  races  of  men,  and  even 
different  families  of  the  same  race,  varv  widelv  in 
these  respects.  And  the  most  important  fact  is  that 
these  characters  of  natural  imnumity  or  susceptibility 
to  one  disease  or  anoth<'r  are  transmissible  ])y  heredity. 
This  fact  serves  to  solve  our  practical  problems. 


112  HEREDITY 

For  instance,  medical  men  now  believe,  as  we  have 
seen,  that  consumption  is  not  hereditary,  but,  on  the 
other  hand,  that  the  "  tendency  "  to  consumption,  or 
the   consumptive  "  diathesis,"  or  the  higher   degree 
of    susceptibility   to   the    attacks    of    the    tubercle 
bacillus,  is  hereditary.     On  every  ground  the  dis- 
tinction is  well  worth  making.     In  the  first  place, 
it   now   appears    that    there  is   no  inevitable   curse 
pronounced  upon  the  child  of  the  consumptive.     He 
probably  inherits  from  his  parent  that  special  degree 
of  susceptibility  which  proved  fatal  to  that  parent. 
But   he  has  not  inherited  the  disease  itself.     And 
let  us  recall  the  chapter  on  the  relative  importance 
of  heredity  and  environment.     The  exceptional  sus- 
ceptibility to  tuberculosis  is  only  a  potentiality,  and 
the  environment  has  the  power  of  developing,  or  sup- 
pressing, or   modifying  it.     Thus  the  child  of  the 
consumptive  may  live  in  such  an  environment — I 
am  tempted  to  say  that  environment  in  this  place 
practically   means   open    bedroom   windows — as    to 
suppress   this   potential   susceptibility,  and  he  may 
indeed,  though  he  has  inherited  this  malign  poten- 
tiality, acquire  a  high  degree  of  immunity.     I  speak 
of  the   specific    case,  not   of  all  microbic   diseases. 
But  it   is   evident    that    the   practical  problem   for 
the   child  of  the  consumptive  is   not   patiently  to 
await  an  inevitable  doom,  but  to  overcome  heredity 
by  environment — in  his  case  notably  the  atmospheric 
environment. 

In  the  second  place,  the  distinction  between  the 
inheritance  of  a  disease  and  the  inheritance  of  a 
susceptibility  to  the  attacks  of  an  external  cause 
of  disease  is  worth  making,  because  of  its  bearing 


HEREDITY    AND    DISEASE  11  .'i 

upon  social  as  well  as  individual  practice.  If  it 
could  be  demonstrated,  for  instance,  that  the  sus- 
ceptibility to  certain  grave  diseases  is  confined  to 
certain  members  of  the  community,  who  inevitably 
transmit  it  to  their  children,  we  might  well  regard 
it  as  a  duty  to  interfere  with  the  reproduction  of 
those  persons — as  would  the  disease  itself,  in  accord- 
ance with  the  law  of  natural  selection. 

In  the  third  place,  it  is  of  importance  to  consider 
whether  susceptibility  to  a  disease  acquired  -by  an 
individual  can  be  transmitted  to  his  otispring  as  an 
actual  part  of  the  germinal  inheritance.  But,  in  brief, 
it  may  be  said  that  the  study  of  heritability  of  disease 
does  not  reveal  any  exceptions  to  the  laws  of  heredity 
observed  in  normal  cases. 

Having  excluded  so  many  familiar  cases  as  not 
properly  to  be  called  facts  of  inheritance,  let  us 
now  consider  the  true  cases  of  the  inheritance  of 
disease. 

And,  first  of  all,  let  us  note  the  existence  of  certain 
nervous  abnormalities  which  are  inherited.  Merely 
mentioning  the  peculiar  case  of  FricdreicJis  or 
Hereditary  ataxia,  which  is  usually  seen  in  several 
children  of  one  family,  and  is  certainly  of  germinal 
origin,  but  is  not  found  in  their  parents,  we  may 
say  that  definite  nervous  disordia-s  are  not  inherited, 
but  that  various  disorders  may  arise  in  consequence 
of  the  inheritance  of  an  instability  or  tendency  to 
disease  of  the  nervous  system.  Dipsomania,  for 
instance,  is  not  inherited ;  but  the  state  of  the 
nervous  system  which  leads  to  dipsomania  in  the 
father  may  often  be  transmitted  to  his  son.  If, 
however,  the  alcoholic  habit  is  acquired  as  the  result 

II 


114  HEREDITY 

of  circumstances,  and  does  not  depend  upon  a 
primary  nervous  defect,  there  is  little  reason  to 
believe  that  this  acquirement  is  often  transmitted; 
though  even  Weismann  admits  the  possibility  that 
persistent  nerve  fatigue  may  affect  the  germ-plasm, 
and  so  give  rise  to  neurotic  tendencies  in  the  off- 
s-pring.  The  subject  is  too  large  to  be  dealt  with 
here.  As  to  the  transmission  of  insanity,  this  may 
be  added  to  what  has  already  been  said,  that  "  there 
is  no  clear  case  of  a  normal  subject  becoming  an 
acute  maniac  through  external  shock  and  trans- 
mitting his  disease." 

Lastly,  as  to  those  definite  specific  diseases  which 
are  unquestionably  transmitted.  These  are  of 
germinal  origin.  Highly  typical,  and  of  very  great 
interest  in  relation  to  the  discoveries  of  Mendel/ 
are  the  "  bleeding  disease,"  or  haemophilia,  and 
colour-blindness.  These  usually  show  themselves 
in  males,  but  are  transmitted  by  females.  For 
instance,  a  colour-blind  man  had  two  normal 
daughters,  each  of  whom  had  one  colour-blind  son, 
whose  three  normal  daughters  had  four  colour-blind 
sons,  and  so  on,  until  in  the  sixth  generation  there 
were  eight  males,  of  whom  seven  were  colour-blind. 
Similar  genealogical  trees,  in  cases  of  both  of  these 
diseases,  might  be  multiplied  without  limit.  Abnor- 
malities, such  as  the  occurrence  of  six  fingers  or 
toes,  may  also  be  traced  through  as  many  as  half-a- 
dozen  generations. 

1  See  Chapter  VIL 


MENTAL    HEliEDlTY  llj 

CHAPTER    XIV 

MENTAL     HLKEDITY 

This  concluding  chapter  is  merely  a  brief  adden- 
dum, added  for  the  sake  of  formal  completeness. 
The  facts  of  mental  heredity  are  dealt  with  at  leni^th 
in  the  volume  on  psychology.  Thanks  to  the  epoch- 
making  work  of  Herbert  Spencer,  the  psychology 
of  to-day  is  essentially  an  evolutionary  or  genetic 
science.  The  leading  problems  of  psychology  are 
problems  in  mental  inheritance.  From  the  point  of 
vie^v  ot  biology  proper,  we  recognise  the  unques- 
tionable inheritance,  in  all  animals  that  possess  a 
nervous  system,  of  a  nervous  organisation  which  is 
intimately  correlated  with  the  facts  of  mind  and 
consciousness.  Nearly  all  the  questions  discussed 
in  the  preceding  pages  have  an  immediate  bearing 
on  psychology.  One  of  the  chief  problems  of  the 
psychologist,  for  instance,  is  as  to  the  existence  of 
innate  ideas,  or  ideas  or  "  modes  of  consciousness," 
or  "forms  of  thought,"  which  are  independent  of 
experience.  The  question  arises  whether  these 
ideas  are  independent  of  individual  experience  but 
dependent  upon  racial  experience.  This  doetrine 
would  appear  to  imply  something  very  like  the 
inheritance  of  acquired  characters. 

All  that  must  be  insisted  on  here,  however,  is  that 
the  physical  characters  of  the  brain  antl  spinal  cord 
and  system  of  nerves  are  subject  to  the  same  laws 
of  inheritance  as  the  physical  characters  of  the 
limbs,  or  the  skeleton,  or  the  internal  organs.     Pro- 


116  HEREDITY 

fessor  Pearson  has  indeed  shown  that  the  facts  of 
inheritance  of  mental  and  moral  characters  seem  to 
be  precisely  parallel  to  the  facts  of  inheritance  of 
physical  characters.  The  explanation  of  this  paral- 
lelism is  doubtless  to  be  found  in  the  interdependence 
of  psychical  and  physical  characters. 

But  I  hope  to  make  it  plain  in  the  volume  on 
psychology  that  adequately  to  discuss  the  subject 
of  mental  heredity  would  be  to  write  a  treatise  upon 
the  principles  of  modern  psychology.  Such  a  task 
is  not  to  be  attempted  as  an  appendix  to  a  discussion 
of  heredity  in  general. 


SUBJECT     INDEX 


Acquirements,  15,  74 
Amphimixis,  32 
Atavism,  64 
Chromatin,  19 
Determinants,  20 
Dominant  characters,  64 
Environment,  71 
Gametes,  24 
Germ-cells,  24 
Germ-plasm,  27 
Heredity,  definition  of,  9 
evolutionary   importance 

of,  13 
Homogamy,  35 
Law  and  cause — their  nature, 

48 


Law  of  ancestral  inheritance, 
42 

Law  of  regression  to  medio- 
crity, 36 

Law  of  segregation,  63 

Mutation,  63 

Pangenesis,  68 

Parthenogenesis,  28 

Physiological  units,  22 

Recapitulation  theory,  66 

Recessive  characters,  64 

Telegony,  81 

Variation,  10,  29,  ttc. 

progressive  and  regres- 
sive, 33 


[Indkx  to  NAMita 


U7 


INDEX    TO    NAMES 


Bateson,  58 
Darwin,  35,  68 
Ehrlich,  107 
Ellis,  Havelock,  98 
Ewart,  Cossar,  65 
Galton,  36,  42 
Haeckel,  66,  83 
Hertwig,  69 
Hall,  William,  92 
Lamarck,  74 
Mackenzie,  Leslie,  93 


Mendel,  58,  60 
Mitchell,  Chalmers,  65 
Pearson,  Karl,  34 
Reid,  Archdall,  15,  33,  66 
Spencer,  13,  21,  56,  89,  115 
Thomson,  25,  65 
Vernon,  55,  77 
Vries,  De,  61 
Weismann,  19,  26,  31,  54, 

73 
Weldon,  53 


Printed  by  Ballantyne,  Hanson  ^r'  Co. 
Edinburgh  <S-^  London 


A^ 


OCT  2  0  1999 


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